A New Sesquiterpene Lactone from Ainsliaea bonatii

A new sesquiterpene lactone, Ainsliaolide A, was isolated from Ainsliaea bonatii. The structure was determined on the basis of spectral data.     

Speciation in the aqueous H+/H2VO4-/H2O2/picolinate system relevant to diabetes research

A detailed study of the quaternary aqueous H+/H2VO4-/H2O2/picolinate (Pi-) system has been performed at 25 degrees C in 0.150 M Na(Cl) medium using quantitative 51 V NMR (500 MHz) and potentiometric data (glass electrode). In the ternary H+/H2VO4-/Pi- system, six complexes have been found in the pH region 1-10. In the quaternary H+/H2VO4-/H2O2/Pi- system, eight additional complexes have been found. Generally, equilibria are fast in both systems. The rate of peroxide decomposition depends on the species in solution. Chemical shifts, compositions and formation constants for the species are given. Equilibrium conditions and the fit of the model to the experimental data are illustrated in distribution diagrams. Possible formation of mixed ligand species with imidazole, lactic acid and citric acid have been investigated and ruled out under the same experimental conditions. Structural proposals are given, based on 1)C NMR data and available crystal structures.     

The Influence of Cobalt (II) in Carboxymethyl Cellulose Processing

Controlling the reduction in molecular weight of the cellulose chains is essential in the production of carboxymethyl cellulose (CMC). Such a reduction can be achieved by the addition of cobalt during the process of cobalt(II) ions, which act as a catalyst for oxidative cleavage, and the influence thereof has been studied under a variety of conditions. This study has resulted in a model that summarises the effects of the added amount of cobalt, the time for the cobalt reaction, the temperature in the mercerisation stage of the CMC-manufacturing process and finally the effect of the temperature in the etherification stage. It is shown that it is important for cobalt to be present during the mercerisation stage in order to achieve the desired viscosity.     

Recoil spectrometry: Ion accelerator based elemental characterisation of surface layers

Recoil Spectrometry covers a group of techniques that are very similar to the well known Rutherford backscattering Spectrometry technique, but with the important difference that one measures the recoiling target atom rather than the projectile ion. This makes it possible to determine both the identity of the recoil and its depth of origin from its energy and velocity, using a suitable detector system. The incident ion is typically high-energy (30–100MeV)³⁵C1,⁸¹Br or¹²⁷I. Low concentrations of light elements such as C, O and N can be profiled in a heavy matrix such as Fe or GaAs. Here we present an overview of mass and energy dispersive recoil Spectrometry and illustrate its successful use in some typical applications.     

DFT Study on the Structure of Ionic Liquid 1-Ethyl-3-methylimidazolium Hexafluorophosphate

1 INTRODUCTION Ionic compounds generally have high melting points and always exist in solid state since they are main- tained by electrovalent bonds. Ionic Liquids (ILs), which are liquids at or near ambient temperature, have been a class of ionic compounds extensively studied experimentally and theoretically in recent years[1, 2]. ILs consist exclusively of anions and ca- tions and do not contain any neutral molecule. They have many attractive properties, such as low vapor pressure, no…     

ABSORPTION SPECTRAL SHIFTS OF CAROTENOIDS RELATED TO MEDIUM POLARIZABILITY

Abstract–Solvent induced absorption spectral shifts of the electronic transition from ground 1 A_g state to the excited 1B_u state in carotenoids have been studied. It is shown that the shift depends only on dispersion interactions in non-polar solvents. In polar media there is just a small extra contribution to the red-shift, due to other forms of interactions. The spectral shifts are well described by the theory, which expresses the shift relative to the gas phase value, as a function of solvent polarizability. The main conclusion is that the dominating mechanism behind the large red-shifted absorbance of carotenoids in the proteinacous environment, in vivo, is the mutual polarizability interactions between the carotenoids and the surrounding medium. The solution-phase values of the dipole moments of the lA_g to 1B_u transitions and the differences of isotropic polarizability between 1B_u and lA_g states of carotenoids in non-polar solvents are calculated and found to be around 13 D and 360 ų respectively. From the great overlap of absorption spectra between carotenoids in quinoline and carotenoids in vivo in purple bacterial antenna complexes, it can be expected that the carotenoids are surrounded by several aromatic amino acids in vivo. Comparisons have been done between the exicted states in carotenoids and in linear conjugated polyenes.     

Unusual effects of separation conditions on chiral separations

Unusual effects in liquid chromatographic separations of enantiomers on chiral stationary phases are reviewed with emphasis on polysaccharide phases. On protein phases and Pirkle phases reversal of the elution order between enantiomers due to variation of temperature and mobile phase composition has been reported. Most of the nonanticipated observations have dealt with the widely used polysaccharide phases. Reversed retention order and other stereoselective effects have been observed by variation of temperature, organic modifier and water content in nonpolar organic mobile phases.     

A modified standard addition method in X-ray fluorescence spectrometry

A modified standard addition method for single element determination by X-ray fluorescence spectrometry has been studied. The attenuation properties of the standard added samples are kept constant by adding decreasing amounts of an attenuation modifier along with increasing amounts of a standard. In this way the standard addition curve will be a straight line in cases where the ordinary standard addition curve is non-linear, and linear regression can be used to evaluate the concentration of the analyte. Standard additions of oxides of a number of elements, with and without modifier, have been made to cellulose powder or a mixture of aluminium oxide and polyethylene as matrices in order to test the method. The method has been applied to the determination of zinc in fly-ash from a steel work and of iron in cement. The fly-ash contained about 5% of zinc and the cement samples between 2 and 5% of Fe(2)O(3). The results were compared with those obtained by ICP-AES after decomposition of samples in lithium tetraborate or lithium metaborate and dissolution of the melt in 10%(v/v) nitric acid. The results agreed within 2%, relative, for fly-ash and within 3-6%, relative, for cement samples.     

Chemoenzymatic Synthesis of Cellular Adhesion Tripeptide RGD Precursor in Organic Media

IntroductionA characteristic tripeptide sequence Arg-Gly-Asp(RGD) that is found within fibronectin and other rela-ted adhesion molecules in extracellular matrices(ECM)has received considerable attention from researcherssince it was proved to be a recognit…     

Dissociative recombination of the weakly bound NO-dimer cation: cross sections and three-body dynamics

Dissociative recombination (DR) of the dimer ion (NO)(2) (+) has been studied at the heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory, Stockholm. The experiments were aimed at determining details on the strongly enhanced thermal rate coefficient for the dimer, interpreting the dissociation dynamics of the dimer ion, and studying the degree of similarity to the behavior in the monomer. The DR rate reveals that the very large efficiency of the dimer rate with respect to the monomer is limited to electron energies below 0.2 eV. The fragmentation products reveal that the breakup into the three-body channel NO+O+N dominates with a probability of 0.69+/-0.02. The second most important channel yields NO+NO fragments with a probability of 0.23+/-0.03. Furthermore, the dominant three-body breakup yields electronic and vibrational ground-state products, NO(upsilon=0)+N((4)S)+O((3)P), in about 45% of the cases. The internal product-state distribution of the NO fragment shows a similarity with the product-state distribution as predicted by the Franck-Condon overlap between a NO moiety of the dimer ion and a free NO. The dissociation dynamics seem to be independent of the NO internal energy. Finally, the dissociation dynamics reveal a correlation between the kinetic energy of the NO fragment and the degree of conservation of linear momentum between the O and N product atoms. The observations support a mechanism in which the recoil takes place along one of the NO bonds in the dimer.