Antioxidant activity of (+)-bergenin: a phytoconstituent isolated from the bark of Sacoglottis uchi Huber (Humireaceae)

(+)-Bergenin (1) was isolated from Sacoglottis uchi, a species of vegetable found in the Amazon region and popularly used for the treatment of several hepatic problems. The structure of 1 was fully characterized using IR, GC-MS and NMR (1D and 2D) analyses. This phytoconstituent has been used as an oriental folk medicine for the treatment of many diseases and shows antihepatotoxic properties. Tests with beta-carotene, DPPH and a heterogeneous Fenton system were carried out, confirming the antioxidant activity of 1. Theoretical calculations were performed to investigate the formation of the radical derivatives of 1 using *H, *OH, *CH(3), and *CCl(3) as initiator radicals. DFT thermodynamic calculations showed that the methoxyl group (O-6-CH(3)) is the most favorable site for radical attack. Frontier molecular orbital analysis showed that nucleophilic radical attack is favored on the aromatic ring of 1 where the LUMO is localized, with antibonding character with respect to the O-6-CH(3) bond. The possibilities of attack at other sites on 1 were investigated in detail in order to understand the regiospecificity of this reaction.     

Semi-empirical topological index: development of QSPR/QSRR and optimization for alkylbenzenes

The semi-empirical topological index, I(ET), was developed and optimized to describe the chromatographic retention of alkylbenzenes on the squalane stationary phase. The simple linear regression between the chromatographic retention and the proposed index, for 122 alkylbenzenes studied, is of good quality (determination coefficient, r(2)=0.9996, standard deviation, S.D.=5.5, and leave-one-out cross-validation correlation coefficient, r(CV)(2)=0.9996). The predictive ability of I(ET) was also verified for stationary phases with two different polarities (SE-30 and Carbowax 20 M), and good results were obtained, especially for the stationary phase with low polarity, showing that the specific molecular interactions occur on highly polar phases. The I(ET) was applied to construct quantitative structure-property relationship (QSPR) models for representative properties such as boiling point, Bp(degrees C), octanol/water partition coefficient, log P, van der Waals volume (V(W)) and molar refractivity (R(M)). Satisfactory quality QSPR models were obtained with Bp, V(W) and R(M) showing that the molecular size and dispersive forces are dominating factors with respect to the chromatographic retention.     

Imidazolium-based zwitterionic surfactant: a new amphiphilic Pd nanoparticle stabilizing agent

Palladium nanoparticles (NPs) with an average size of 3.4 nm were prepared in water using imidazolium-based surfactant 3-(1-dodecyl-3-imidazolio)propanesulfonate (ImS3-12) as a stabilizer. The Pd NPs are highly dispersible in water and chloroform and were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, powder X-ray diffraction, and dynamic light scattering. The results indicate that in water the NP surface is covered with a double layer of ImS3-12 molecules. The NPs were effective in the aqueous biphasic hydrogenation of cyclohexene, with easy recycling and no loss of catalytic activity after four successive runs.     

8,9-Methylenedioxy-3,4-dihydro-1,4,5-benzotriazocin-2(1H)-ones

The title compounds are obtained directly on reaction of 6-chloroacetamidopiperonal with substituted phenylhydrazines. Piperonal was used as starting material.     

Double semiconductor substrate in overlay shielded superconducting microstrip lines

The Transverse Transmission Line (TTL) is used in the theory of the overlay shielded microstrip lines considering the superconductor strip on two semiconductor regions. The superconductor effect is included with the boundary condition of the surface impedance, that is related to the complex conductivity of the material, calculated from the advanced two-fluid model. Applying the moment method the complex propagation constant of the structure, including the phase constant and the attenuation constant, is obtained. Results are presented for the complex propagation constant, versus the frequency and the temperature, of this overlay superconducting microstrip lines.     

Quantum transport in periodically δ-doped GaAs

The Shubnikov-de Haas spectra of GaAs samples with a periodical doping with Si were measured at 4.2 K using fields of 0–14 T. From the Shubnikov-de Haas spectrum the quantum mobilities associated with individual minibands were estimated for each sample. The sheet density of Si atoms in each doping plane was fixed at approximately 2.5 × 10¹² cm^?2 in all samples and the doping period was varied in the range 40–1000 Å. The quantum mobilities obtained experimentally are compared with theoretical calculations using the random phase approximation to describe the screened interaction between electrons and charged impurities. The theory describes qualitatively the results of the experiment, i.e. an increase of the quantum mobility with the index of the miniband, and a decrease in the mobility in all minibands when the doping period is made shorter (with a weak maximum at intermediate values of the doping period). Various possible improvements of the model are suggested.     

Tetrataenite in metallic grains of the Antarctic L6 chondrite ALHA 76009

Mössbauer X-ray diffraction and electron microscopy studies revealed that segregation and ordering occurred in the metal particles of the Antarctic L6 chondrite ALHA 76009. The ordered crystal structure of AuCu type (tetrataenite) was detected coexisting with the disordered 50-50 taenite.