Topological transitions in multi-band superconductors

The search for Majorana fermions has been concentrated in topological insulators or superconductors. In general, the existence of these modes requires the presence of spin–orbit interactions and of an external magnetic field. The former implies in having systems with broken inversion symmetry, while the latter breaks time reversal invariance. In a recent paper, we have shown that a two-band metal with an attractive inter-band interaction has non-trivial superconducting properties, if the k$k$-dependent hybridization is anti-symmetric in the wave-vector. This is the case, if the crystalline potential mixes states with different parities as for orbitals with angular momentum l$l$ and l+1$l+1$. In this paper we take into account the effect of an external magnetic field, not considered in the previous investigation, in a two-band metal and show how it modifies the topological properties of its superconducting state. We also discuss the conditions for the appearance of Majorana fermions in this system.     

Topological states in normal and superconducting p-wave chains

We study a two-band model of fermions in a 1d chain with an antisymmetric hybridization that breaks inversion symmetry. We find that for certain values of its parameters, the sp-chain maps formally into a p-wave superconducting chain, the archetypical 1d system exhibiting Majorana fermions. The eigenspectra, including the existence of zero energy modes in the topological phase, agree for both models. The end states too share several similarities, such as the behavior of the localization length, the non-trivial topological index and robustness to disorder. However, we show that the excitations in the ends of a finite sp chain are conventional fermions though endowed with protected topological properties. Our results are obtained by a scattering approach in a semi-infinite chain with an edge defect treated within the T-matrix approximation. We present exact numerical diagonalization results that extend our analysis to arbitrary parameters and to disordered systems.     

Chemical composition and antioxidant, antimicrobial, and larvicidal activities of the essential oils of Annona salzmannii and A. pickelii (Annonaceae)

The essential oils from the leaves of Annona salzmannii and A. pickelii (Annonaceae) growing in Sergipe, northeastern region of Brazil, were obtained by hydrodistillation using a Clevenger-type apparatus, and analyzed by GC/MS and GC/FID. Thirty-four compounds were identified in the essential oil of A. salzmannii and twenty-seven in that of A. pickelii; sesquiterpenes predominated in both essential oils. Bicyclogermacrene (20.3%), (E)-caryophyllene (19.9%), delta-cadinene (15.3%), alpha-copaene (10.0%), and allo-aromadendrene (5.7%) were the main components of A. salzmannii, and bicyclogermacrene (45.4%), (E)-caryophyllene (14.6%), and alpha-copaene (10.6%) of A. pickelii. The essential oils showed significant antioxidant capacity in the ORAC(FL) and DPPH assays. The antimicrobial activity of these essential oils was also evaluated against bacteria and fungi, as well as the larvicidal activity against Aedes aegypti larvae.     

Multivariate optimization of the determination of zinc in diesel oil employing a novel extraction strategy based on emulsion breaking

This paper describes the extraction/pre-concentration of Zn from diesel oil and its determination by Flame Atomic Absorption Spectrometry (FAAS), proposed as a novel approach for these kinds of analyses and the multivariate optimization of the proposed procedure. The extraction of Zn is based on the emulsification of an aqueous solution containing Triton X-114 and HNO₃ with diesel oil samples followed by breaking of the emulsion by heating. The aqueous phase obtained after the emulsion breaking was collected and used for Zn quantification by FAAS. The methodology was optimized using a Doehlert design and the system variables were the concentrations of surfactant and HNO₃ in the solution employed in the emulsification and the temperature used in the emulsion breaking. The ratio between absorbance and the time required to break the emulsions was taken as response. Two sets of experiments, using different emulsifier agents, were run: the first one using Triton X-100 and the second one using Triton X-114. At optimized conditions, the emulsions were prepared by mixing 10 mL of diesel oil with 2 mL of a solution containing 5% w/v of Triton X-114 and 15% v/v of HNO₃ and broken by heating at 80 °C. The proposed analytical procedure was applied in the analysis of six real samples of diesel oil and a recovery test was carried out by spiking the samples with known amounts of Zn (25 and 50 μg L⁻¹), added as organometallic oiled standard. Recovery percentages achieved in this test were between 92 and 109%.     

Synthesis of (Carbo)nucleoside Analogues by [3+2] Annulation of Aminocyclopropanes

(Carbo)nucleoside derivatives constitute an important class of pharmaceuticals, yet there are only few convergent methods to access new analogues. Here, we report the first synthesis of thymine‐, uracil‐, and 5‐fluorouracil‐substituted diester donor–acceptor cyclopropanes and their use in the indium‐ and tin‐catalyzed [3+2] annulations with aldehydes, ketones, and enol ethers. The obtained diester products could be easily decarboxylated and reduced to the corresponding alcohols. The method gives access to a broad range of new (carbo)nucleoside analogues in only four or five steps and will be highly useful for the synthesis of libraries of bioactive compounds.     

New trifluoromethyl triazolopyrimidines as anti-Plasmodium falciparum agents

According to the World Health Organization, half of the World's population, approximately 3.3 billion people, is at risk for developing malaria. Nearly 700,000 deaths each year are associated with the disease. Control of the disease in humans still relies on chemotherapy. Drug resistance is a limiting factor, and the search for new drugs is important. We have designed and synthesized new 2-(trifluoromethyl)[1,2,4]triazolo[1,5-a]pyrimidine derivatives based on bioisosteric replacement of functional groups on the anti-malarial compounds mefloquine and amodiaquine. This approach enabled us to investigate the impact of: (i) ring bioisosteric replacement; (ii) a CF? group substituted at the 2-position of the [1,2,4]triazolo[1,5-a]pyrimidine scaffold and (iii) a range of amines as substituents at the 7-position of the of heterocyclic ring; on in vitro activity against Plasmodium falciparum. P. falciparum dihydroorotate dehydrogenase (PfDHODH) through strong hydrogen bonds. The presence of a trifluoromethyl group at the 2-position of the [1,2,4]triazolo[1,5-a]pyrimidine ring led to increased drug activity. Thirteen compounds were found to be active, with IC?? values ranging from 0.023 to 20 μM in the anti-HRP2 and hypoxanthine assays. The selectivity index (SI) of the most active derivatives 5, 8, 11 and 16 was found to vary from 1,003 to 18,478.     

Improving the radiochemical purity determination of 123I-labeled metaiodobenzylguanidine

The HPLC method originally applied at the Nuclear Engineering Institute (IEN) for the radiochemical purity determination of ¹²³iodine labeled m-iodobenzylguanidine (¹²³I-mIBG) takes 18.5 min. The final product release also depends on this result, and to facilitate this stage, we aimed to decrease this analysis time. We also intended to use fewer toxic compounds, if feasible. The optimization approach used herein was a combination of factorial and mixture designs to study simultaneously the selected variables. Analysis time, resolution and chromatograms aspect were the measured responses. The qualitative analysis of these responses provided the best chromatographic separation conditions that were 52 mM KH₂PO₄ in a solution of ethanol and water (1:1), applying a flow rate of 0.50 mL min^?1 and C18 column (4.6 × 250 mm, 5 μm). These optimum conditions not only decreased the analysis time in 61 %, but also allowed the reduction of mobile phase toxicity. To assure reliable data, method validation was performed for these conditions. The method has proved its specificity, the detection limit found was 3.70 × 10^?4 MBq mL^?1 and the quantification limit has corresponded to 1.11 × 10^?3 MBq mL^?1. Repeatability and intermediate precision has not exceeded 3 and 5 %, respectively, and the accuracy has matched the interval of 95–105 %. This new method has been routinely applied in the radiochemical purity determination of ¹²³I-mIBG at IEN.     

Mercapto-modified copolymers in polymer blends, 1. Functionalization of EPDM with mercapto groups and its use in NBR/EPDM blends

Ethylene-propylene-diene rubber (EPDM) was reacted with thioacetic acid in the presence of 2,2′-azoisobutyronitrile (AIBN), giving rise to thioacetate-modified EPDM (EPDMTA). The extent of the incorporation was studied as a function of both thioacetic acid and AIBN concentration and reaction time. The products were analyzed by FTIR spectroscopy, sulfur content, and ¹H NMR spectroscopy. The hydrolysis of EPDMTA in a NaOH methanolic solution resulted in mercapto-modified EPDM (EPDMSH). The addition of 5 wt.-% of this functionalized copolymer to a sulfur-vulcanized nitrile rubber (NBR)/EPDM (70 : 30 wt.-%) blend accelerated the vulcanization process as indicated by oscillating disk rheometer analysis. In addition, an improvement of mechanical and ageing properties was also observed.