A new ent-labdane eiterpenoid lactone from Andrographis paniculata

A new ent-labdane diterpenoid lactone with a new natural product was isolated from Andrographis paniculata. Their structures were elucidated on the basis of spectral evidences including 2D NMR.     

Saturation effects in the photoluminescence spectra of Hg0.3Cd0.7Te

The photoluminescence spectrum of Hg_0.3Cd_0.7Te at 77K consists of a narrow, high energy free exciton line D and a broad, low energy deep level E. As a function of incident excitation power, the E line must be saturated before the D line can be observed. We have constructed a simple model that agrees well with the experimental dependences of the luminescence intensities of the D and E lines on excitation power.     

STRAFI imaging of solids: The spatial resolution for quadrupolar nuclei withI=3/2

The density matrix formalism has been used for computer calculations of the thickness of the excited slice, which determines the spatial resolution, in the case of quadrupolar nuclei havingI=3/2, for varying values of the electric quadrupolar coupling constant and the pulse-duration, when the spins are placed in a very strong magnetic field-gradient (50 T/m).     

Optimization and validation of arsenic determination in foods by hydride generation flame atomic absorption spectrometry

A hydride generation flame atomic absorption spectrometric method was developed and optimized to quantitate arsenic (As) in foods. A wet digestion of the samples with HNO3 + H2O2 was performed and excess oxidants were eliminated by addition of hydrochloric acid and urea. As5+ in As3+ was then reduced by potassium iodide. The As3+ solution was analyzed by generation of arsine with sodium tetrahydroborate. As determination ranged from 2.5 to 20 microg/L, with a determination coefficient of 0.997. The limits of detection (LOD) and quantitation (LOQ) were 0.6 and 2.1 microg/L, respectively. The method was validated and good results were obtained for recovery, precision, accuracy, LOD, and LOQ. This method is now used to analyze foods from Rwanda.     

Ab initio calculations of the electronic structure of helical polymers

An ab initio self-consistent-field (SCF ) algorithm taking into account all the features of the one-dimensional translational periodicity and the helical symmetry is presented. This algorithm includes the long-range correction to the Coulomb potential and is designed to calculate the band structure of periodic one-dimensional polymers (planar or helical). Its efficiency in terms of computing time and numerical accuracy is tested via applications on a (LiH)_n chain, polyethylene, and four conformers of polypropylene.     

Über Heptacetylchlormilchzucker

Ohne Zusammenfassung     

PEG-400 as an efficient reaction medium for the synthesis of 2,4,5-triaryl-1H-imidazoles and 1,2,4,5-tetraaryl-1H-imidazoles

An efficient protocol for the one-pot multicomponent synthesis of various 2,4,5-triaryl- IH-imidazoles and 1,2,4,5-tetraaryl-1H-imidazoles using PEG-400 as reaction medium is described. This method has the advantages of good yields, less pollution and simple reaction conditions.     

Time-dependent numerical simulation of viscoelastic flow and stability

The 4×4 mixed finite-element method is extended in order to calculate time-dependent viscoelastic flow. The basic algorithm uses a fully implicit technique with a predictor-corrector control of the time step for monitoring the accuracy. Excellent agreement is found with analytical test cases. Several decoupled schemes are also developed with a view to reducing the cost of the time-dependent calculations. However, none of them reaches that goal on actual flow problems because of a drastic reduction of the time step.The time-dependent algorithm is used for verifying the stability of steady-state viscoelastic flow solutions. The approach consists of using a steady-state solution as a set of initial conditions for a time-dependent algorithm with the hope that, in case of instability, the system will lead to a stable solution. More precisely, we consider the flow of an Oldroyd-B fluid through a four-to-one contraction. Starting from a steady-state flow, we impose a pressure impulse in the entry section and calculate the approach toward another steady-state. For planar contractions, we do not constrain the flow to be symmetric while, for circular contractions, the flow is endowed with swirling capabilities. It is found that the stable or unstable character of the flow depends upon the mesh as well as upon the method of discretization.     

A new free recoverable and reusable mono-alkaloid-type ligand and its use in preparation of ethyl （2R,3S）-2,3-dihydroxy-3-phenylpropionate

A new free recoverable and reusable mono-alkaloid-type ligand has been synthesized by a simple method.With highly polar groups,the ligand can be recycled and reused eight times to prepare ethyl(2R,3S)-2,3-dihydroxy-3-phenylpropionate with high yield and ee via asymmetric dihydroxylation(AD) reaction.     

Rapid Synthesis of Porous Honeycomb Cu/Pd through a Hydrogen‐Bubble Templating Method

A rapid electrochemical method based on using a clean hydrogen‐bubble template to form a bimetallic porous honeycomb Cu/Pd structure has been investigated. The addition of palladium salt to a copper‐plating bath under conditions of vigorous hydrogen evolution was found to influence the pore size and bulk concentration of copper and palladium in the honeycomb bimetallic structure. The surface was characterised by X‐ray photoelectron spectroscopy, which revealed that the surface of honeycomb Cu/Pd was found to be rich with a Cu/Pd alloy. The inclusion of palladium in the bimetallic structure not only influenced the pore size, but also modified the dendritic nature of the internal wall structure of the parent copper material into small nanometre‐sized crystallites. The chemical composition of the bimetallic structure and substantial morphology changes were found to significantly influence the surface‐enhanced Raman spectroscopic response for immobilised rhodamine B and the hydrogen‐evolution reaction. The ability to create free‐standing films of this honeycomb material may also have many advantages in the areas of gas‐ and liquid‐phase heterogeneous catalysis.