Modulation of HTSC characteristics induced by proton irradiation

Il Nuovo Cimento D - Bulk slabs of sintered YBCO were irradiated with monoenergetic protons at different energies (3.5 and 6.5 MeV) and different fluences, ranging from 1.8·1016 to...     

New phases in the most basic zone of the system Ba−Cu−O

Summary In the most basic part of the binary system BaO−CuO two new compounds were identified corresponding to the Ba₂CuO₃ and Ba₃CuO₄ formulae. Another more oxidized phase of composition Ba₂CuO_3+δ was also obtained, which can exist in two crystalline modifications. For all these new substances the structural type and the lattice parameters are reported.     

Structural characterization of the ligstroside aglycone isoforms in virgin olive oils by liquid chromatography–high‐resolution Fourier‐transform mass spectrometry and H/Dexchange

A systematic structural characterization of the isomeric forms related to ligstroside aglycone (LA), one of the most relevant secoiridoids contained in virgin olive oils, was performed using reverse phase liquid chromatography with electrospray ionization Fourier‐transform single and tandem mass spectrometry, operated in negative ion mode (RPLC‐ESI(?)‐FTMS and FTMS/MS). The high mass resolution and accuracy provided by the adopted orbital trap mass analyzer enabled the recognition of more than 10 different isomeric forms of LA in virgin olive oil extracts. They were related to four different types of molecular structure, two of which including a dihydropyranic ring bearing one or two aldehydic groups, whereas the others corresponded to dialdehydic open‐structure forms, differing just for the position of a C═C bond. The contemporary presence of enolic or dienolic tautomers associated to most of these compounds, stable at room temperature (23°C), was also assessed through RPLC‐ESI‐FTMS analyses operated under H/D exchange conditions, ie, by using D₂O instead of H₂O as co‐solvent of acetonitrile in the RPLC mobile phase. As discussed in the paper, the results obtained for LA indicated a remarkable structural similarity with oleuropein aglycone (OA), the most abundant secoiridoid of olive oil, whose isoforms had been previously characterized using the same analytical approach.     

Investigation of superconductivity in the Y−Ba−Cu−O system

Summary Experiments are performed to determine the effect of polyphasicity on YBa₂Cu₃O_7−x critical temperature. Results are obtained which show thatT _c fluctuations up to 2 K exist, depending on phase mixing.     

Bidimensional antiferromagnetism in layered NH4FeF4

Summary The compound NH₄FeF₄, characterized by layers of (FeF₆)³⁻ octahedra alternating with NH ₄ ⁺ layers, has been investigated by means of M?ssbauer spectroscopy. Experimental data, which evidentiate an antiferromagnetic order, are compared with the molecular-field model for anisotropic media. Magnetization is found orthogonal to the octahedra layers and the octahedra axes are found to be tilted by 17° with respect to the magnetization direction.

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Riassunto Il composto NH₄FeF₄, caratterizzato da strati di ottaedri (FeF₆)³⁻ alternati con strati NH ₄ ⁺ , è stato studiato con la spettroscopia M?ssbauer. I dati sperimentali, che evidenziano un ordine antiferromagnetico, sono stati interpretati col modello del campo molecolare per mezzi anisotropi. Si è trovato che la magnetizzazione è ortogonale agli strati ottaedrici e che gli assi ottaedrici sono inclinati di 17° rispetto alla direzione di magnetizzazione.

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Резюме С помощью м?ссбауэровской спектроскопии исследуется соединение NH₄FeF₄, характеризующееся слоями (FeF₆)³⁻, которые чередуются с NH ₄ ⁺ слоями. Экспериментальные данные, которые подтверждают антиферромагнитную упоряденность, сравниваются с моделью молекулярного поля для анизотропной среды. Обнаружено, что намагниченность ортогональна октаэдрическим слоям, а октаэдрические оси наклонены под углом 17° к направлению намагниченности.

     

Low-flux neutron irradiation of ceramic YBa2 Cu3O7−δ

Summary Pellets of sintered YBa₂Cu₃O_7−δ with three different oxygen contents have been irradiated with fast neutron beams of energies 6.5, 3.3 and 4.4 MeV at fluences of 7.7·10⁴, 1.3·10⁵ and 1.4·10⁹ n/cm², respectively. The radiation damage has been investigated by comparing the critical temperature (T _c ^mid ), the zero resistivity and the onset temperature before and after neutron irradiation. The critical current has been measured for a few samples in the same experimental conditions. In all transport measurements two different responses to the neutron radiation are observed and discussed.     

Reactivity of 4‐thiothymidine with Fenton reagent investigated by UV‐visible spectroscopy and electrospray ionization mass spectrometry

The reactivity of the sulfur‐containing nucleoside 4‐thio‐(2′‐deoxy)‐thymidine usually abbreviated as 4‐thio‐thymidine, (S⁴‐TdR) under Fenton conditions, ie, in the presence of H₂O₂ and catalytic amounts of Fe(II), was investigated by UV‐vis spectroscopy and electrospray ionization single and tandem mass spectrometry (ESI‐MS and MS/MS). S⁴‐TdR hydroxylated on the S atom was found to be a key reaction intermediate, ultimately leading to (2′‐deoxy)‐thymidine usually abbreviated as thymidine, (TdR) as the main reaction product. This finding was in accordance with the outcome of the reaction between S⁴‐TdR and H₂O₂, previously investigated in our laboratory. On the other hand, the additional presence of ?OH radicals, induced by the Fe(II)/H₂O₂ combination, led to the increased generation of another interesting S⁴‐TdR product, already observed after its reaction with H₂O₂ alone, ie, the covalent dimer including a S? S bridge between two S⁴‐TdR molecules. More importantly, multihydroxylated derivatives of S⁴‐TdR and TdR were detected as peculiar products obtained under Fenton conditions. Among them, a product bearing an OH group both on the methyl group linked to the thymine ring and on the C5 atom of the ring was found to prevail. The results obtained during this study, integrated by those found previously in our laboratory, indicate 4‐thiothymidine as a promising molecular probe for the recognition, through a careful characterization of its reaction products, of the prevailing species among reactive oxygen species (ROS) corresponding to singlet‐state oxygen, hydrogen peroxide, and hydroxylic radical.