Development and implementation of the k0-standardization and other parametric methods of INAA in Cuba. Part I

This paper explains chronologically the implementation of thek ₀-standardization and other parametric methods in Cuba. Fundamental and applied results in the determination of the most important parameters are obtained, using the IBR-2 at Dubna and Triga Mark III at Mexico reactor facilities. Some modifications in the Stoughton-Halpering convention, and its comparison with the modified Westcott and Høgdahl method are presented. The application of the described methods at the CS-ISCTN low flux facility, using the big samples techniques, is presented.     

Promotion of 1,3-dithiolanes using a bentonitic clay as catalyst

The reactions between 1,2-ethandithiol with several carbonylic compounds to form the corresponding 1,3-dithiolanes were performed using a natural clay as promotor. The target molecules are used as reagents to obtain fine chemicals, herbicides, fungicides, and pharmaceutical compounds among others applications. A kinetic study of camphorquinone and 1,2-ethandithiol showed a first-order dependence with 1,2-ethandithiol as well as with camphorquinone. The substrate transformation in percent was found to be dependent with the reaction time, the amount of catalyst, and the reagents concentration. © 2003 Wiley Periodicals, Inc. 15:71–76, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.10215     

Design,synthesis, molecular docking and in vitro evaluation of benzothiazole derivatives as 11β-hydroxysteroid dehydrogenase type 1 inhibitors

Molecular Diversity - 11-Beta hydroxysteroid dehydrogenase type 1 (11β-HSD1) regulates cortisol levels mainly in adipose, hepatic and brain tissues. There is a relationship between the high...     

Study of the evolution of the hyperfine parameters in nanostructured Fe–Mn–Cu system

An unusually large attenuation (approximately 50%) in the low temperature nuclear orientation directional gamma anisotropy from unannealed thermal neutron irradiated single crystal (¹⁶⁰Tb)TbNiAl₄ has been observed in the region of saturation of the second order nuclear orientation coefficient, B₂. It is suggested that the form of the remanent neutron activation recoil damage in unannealed (¹⁶⁰Tb)TbNiAl₄ is fundamentally electric quadrupolar in origin, as opposed to magnetic dipolar.     

Mössbauer Investigation of Fe–Mn–Cu Nanostructured Alloys Obtained by Ball Milling

Fe₇₉Mn₂₁, (Fe₇₉Mn₂₁)₉₀Cu₁₀, and (Fe₇₉Mn₂₁)₈₀Cu₂₀, alloys, prepared by high energy ball milling were characterized by Mössbauer spectroscopy, X-ray diffraction and ac-susceptibility. Results indicate that the Cu addition favors the formation of a FCC phase with two different magnetic states at room temperature, i.e., an antiferromagnetic and a paramagnetic one. Thermal evolution of the Mössbauer spectra revealed the occurrence of a magnetic ordering along a wide temperature range. This behavior is probably related to Fe atoms in FCC-Fe(Mn,Cu) phase having different environments and grain size distribution. Thermal dependence of in-phase ac-susceptibility shows that a long range ordering starts at 240 K for the Fe₇₉Mn₂₁ alloy and shifts towards lower temperatures with the Cu content. These results would reflect a long-range magnetic ordering transition with a distribution of ordering temperatures rather than a blocking process of particle single-domains.     

Electron impact mass spectra of phosphine sulphides and selenides

An electron impact mass spectral study of phosphine sulphides and selenides established the effect of the heteroatom and the role of the ortho substituent in the fragmentation pattern.     

Pressure-induced structural transformations of the Zintl phase sodium silicide

The high-pressure behaviour of NaSi has been studied using Raman spectroscopy and angle-dispersive synchrotron X-ray diffraction to observe the onset of structural phase transformations and potential oligomerisation into anionic Si nanoclusters with extended dimensionality. Our studies reveal a first structural transformation occurring at 8–10 GPa, followed by irreversible amorphisation above 15 GPa, suggesting the formation of Si–Si bonds with oxidation of the Si⁻ species and reduction of Na⁺ to metallic sodium. We have combined our experimental studies with DFT calculations to assist in the analysis of the structural behaviour of NaSi at high pressure.     

Electronic properties of single-walled carbon nanotube networks

We present a study on the electronic behavior of films of as-prepared and purified single-walled carbon nanotubes (SWNTs) and demonstrate the important role that chemical functionalization plays in modifying their electronic properties, which in turn throws further light on the mechanism of action of SWNT-based sensors. Films of electric arc SWNTs were prepared by spraying, and optical spectroscopy was used to measure the effective film thickness. The room-temperature conductivities (sigma(RT)) of thin films deposited from as-prepared and purified SWNTs are in the range sigma(RT) = 250-400 S/cm, and the nonmetallic temperature dependence of the conductivity indicates the presence of tunneling barriers, which dominate the film conductivity. Chemical functionalization of SWNTs with octadecylamine (ODA) and poly(m-aminobenzenesulfonic acid) (PABS) significantly decreases the conductivity; sigma(RT) = 3 and 0.3 S/cm for SWNT-ODA and SWNT-PABS, respectively.