Relative reactivities of 1,2-dicarbonyl compounds towards permanganate in ethanoic acid medium. Mechanism of the oxidation processes

The oxidative behaviour of the 1,2-dicarbonyl compounds, viz., glyoxal, biacetyl and benzil, towards permanganate in ethanoic acid medium in the presence of HClO₄ has been investigated. The reaction is first order with respect to MnO^– ₄, substrate, as well as H⁺. The rate decreases with an increase in ionic strength. Different thermodynamic parameters have been evaluated. The protonated dialdehyde or diketone reacts with permanganate ion to form an intermediate ester which decomposes in a slow step to produce the corresponding carboxylic acid via C—C bond cleavage.     

Synthesis, characterization, and 3D-FDTD simulation of Ag@SiO2 nanoparticles for shell-isolated nanoparticle-enhanced Raman spectroscopy

Au-seed Ag-growth nanoparticles of controllable diameter (50-100 nm), and having an ultrathin SiO(2) shell of controllable thickness (2-3 nm), were prepared for shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Their morphological, optical, and material properties were characterized; and their potential for use as a versatile Raman signal amplifier was investigated experimentally using pyridine as a probe molecule and theoretically by the three-dimensional finite-difference time-domain (3D-FDTD) method. We show that a SiO(2) shell as thin as 2 nm can be synthesized pinhole-free on the Ag surface of a nanoparticle, which then becomes the core. The dielectric SiO(2) shell serves to isolate the Raman-signal enhancing core and prevent it from interfering with the system under study. The SiO(2) shell also hinders oxidation of the Ag surface and nanoparticle aggregation. It significantly improves the stability and reproducibility of surface-enhanced Raman scattering (SERS) signal intensity, which is essential for SERS applications. Our 3D-FDTD simulations show that Ag-core SHINERS nanoparticles yield at least 2 orders of magnitude greater enhancement than Au-core ones when excited with green light on a smooth Ag surface, and thus add to the versatility of our SHINERS method.     

Structural analysis of aristolochic acids and aristolactams by correlations between calculated and experimental <Superscript>13</Superscript>C NMR chemical shifts

Aristolactam AII (1) and aristolochic acid I (2) were employed as examples in choosing the most suitable theoretical methodology for computing carbon chemical shifts (^Calc δ _C) and for the structural elucidations of aristolactams and aristolochic acids. Geometries of 1 and 2 optimized using HF, BLYP, B3LYP, and PBE methods and 6-311++G** basis set were subjected to δ_C calculations and the calculated chemical shifts obtained were correlated with their ¹³C NMR data. Different possibilities were considered (in the gaseous phase, model PCM (DMSO), and for dimeric systems 1-1 and 2-2), and an explicit solvent (DMSO) model employing BLYP/6-31G* calculations was determined to be the most efficient (R ² = 0.99631 and 0.97713, for 1 and 2, respectively).     

Synthesis of ultrathin and compact Au@MnO2 nanoparticles for shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS)

Shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) based on Au@SiO₂ or Au@Al₂O₃ nanoparticles (NPs) shows great potential to break the long‐standing limitations of substrate and surface generality of surface‐enhanced Raman scattering (SERS). However, the shell of SiO₂ or Al₂O₃ can easily be dissolved in alkaline media, which limits the applications of SHINERS in alkaline systems. Besides that, the synthesis of Au@SiO₂ NPs can be further simplified and Au@Al₂O₃ NPs be replaced by other NPs that are more amenable for mass production. In an attempt to make SHINERS NPs available in any systems practically, we report the synthesis of ultrathin and compact Au@MnO₂ NPs. The shell thickness of MnO₂ can be controlled down to about 1.2 nm without any pinhole. SHINERS based on such Au@MnO₂ NPs exhibits much higher Raman enhancement effect than Au@SiO₂ NPs and can be applied in alkaline systems in which Au@SiO₂ or Au@Al₂O₃ NPs cannot be applied. Copyright © 2011 John Wiley & Sons, Ltd.     

The permeation of nalmefene hydrochloride across different regions of ovine nasal mucosa

The permeability of nalmefene hydrochloride (NH) across different regions of ovine nasal mucosa was investigated in vitro. Five different regions of ovine nasal mucosa (superior turbinate mucosa, middle turbinate mucosa, inferior turbinate mucosa, posterior septum mucosa, and anterior septum mucosa) were studied. The results showed that the permeability coefficients of NH through different regions of nasal mucosa were different, and the suitable regions for the absorption of NH were the middle turbinate mucosa, the posterior septum mucosa and the superior turbinate. At the same time, the middle turbinate mucosa was the largest region among the five regions, thus it was the main absorption region for NH. The high uniformity of the middle turbinate mucosa also made it the most suitable model for the permeation of NH in vitro.     

Validation of a high-performance thin-layer chromatography/densitometry method for the quantitative determination of glucosamine in a herbal dietary supplement

Two-dimensional gas chromatography coupled to triple quadrupole mass spectrometry (GC-GC-MS-MS) is presented as a robust, selective and sensitive method for the accurate quantification of enantiomeric fractions (EFs) of atropisomeric polychlorinated biphenyls (PCBs) in a range of environmental matrices. The method was subjected to a set of quality control and validation experiments. EF precision of the atropisomers 95, 149, 132, and 174 ranged from 0.7 to 1.4% in soil samples. Quantified amounts of these congeners in soil and compost samples (59相似文献   

Physical mapping of 18S rDNA cistron in species of the Omophoita genus (Coleoptera,Alticinae) using fluorescent in situ hybridization

Alticinae has the greatest amount of biodiversity among the Chrysomelidae, with 40,000 described species, only 290 of which have been analyzed cytogenetically. The majority of studies refer to conventional staining and few species have been analyzed or have responded to differential staining methods. The aim of the present study was to describe an 18S rDNA probe for Alticinae and the location of this cluster in species of the Omophoita genus. The fragment of approximately 750 bp obtained through a PCR (Polymerase Chain Reaction) amplification reaction with specific oligonucleotides to 18S rDNA was cloned and denominated pTZ_Ooct_18Sp and then submitted to automatic sequencing. The alignment of the sequences obtained through the sequencing of the clones generated a consensus sequence of 722 bp for Omophoita octoguttata with 98% homology with other species of Alticinae. The analysis of mitotic cells of O. octoguttata and Omophoita magniguttis submitted to fluorescent in situ hybridization (FISH) with the 18S rDNA probe revealed that the ribosomal genes are located in 6th pair. O. magniguttis also has a second labeled pair. Omophoita personata exhibited nucleolar organizer regions associated to one autosome pair. The analysis of meiotic cells submitted to FISH revealed one labeled bivalent in metaphase I in O. octoguttata and O. personata and in one chromosome in metaphase II in O. octoguttata. FISH data suggest a conserved pattern in the species analyzed and an apomorphy of O. magniguttis karyotype. The rDNA 18S probe could be considered an important marker to evidence the karyotypic differentiation, not observed with conventional methodologies, in species considered karyotypically conserved and uniform.     

Period-adding bifurcations and chaos in a bubble column

We obtained period-adding bifurcations in a bubble formation experiment. Using the air flow rate as the control parameter in this experiment, the bubble emission from the nozzle in a viscous fluid undergoes from single bubbling to a sequence of periodic bifurcations of k to k+1 periods, occasionally interspersed with some chaotic regions. Our main assumption is that this period-adding bifurcation in bubble formation depends on flow rate variations in the chamber under the nozzle. This assumption was experimentally tested by placing a tube between the air reservoir and the chamber under the nozzle in the bubble column experiment. By increasing the tube length, more period-adding bifurcations were observed. We associated two main types of bubble growth to the flow rate fluctuations inside the chamber for different bubbling regimes. We also studied the properties of piecewise nonlinear maps obtained from the experimental reconstructed attractors, and we concluded that this experiment is a spatially extended system.     

Perturbative approach to the hydrogen atom in a strong magnetic field

We consider states of the hydrogen atom with the principal quantum number n≤3 and zero magnetic quantum number in a constant homogeneous magnetic field ?. The perturbation theory series is summed using the Borel transformation and conformal mapping of the Borel variable. Convergence of the approximate energy eigenvalues and their agreement with the corresponding existing results are observed for external fields up to n³?/?₀～5, where ?₀ is the atomic magnetic field. The possibility of restoring the asymptotic behavior of energy levels using perturbation theory coefficients is also discussed.