Pollution of agricultural crops with lanthanides,thorium and uranium studied by instrumental and radiochemical neutron activation analysis

The lanthanide elements, Th and U were measured in soils and agricultural crops collected in an area polluted by emissions from a phosphate fertilizer plant. Concentrations of the above elements in the soil and crop samples were determined by instrumental neutron activation analysis (INAA). Selected crop samples were also analyzed using radiochemical neutron activation analysis (RNAA) based on alkaline-oxidative fusion of the irradiated samples followed by precipitation of REE oxalates. Elevated levels of lanthanides, Th and U were found in some samples, especially in wheat chaff and parsley.     

The synthesis and polymerization behavior of bimetallic pyridine diamide complexes containing transition metal (Ti,Zr)

Titanium and zirconium complexes with a pyridine diamide ligand, [2,6-(RNCH₂)₂NC₅H₃]²⁻ (PDMP; R = 2,6-dimethylphenyl) have been synthesized and their catalytic behaviors investigated for ethylene polymerization. It was found that the zirconium complexes, [PDMP]ZrCl₂ (7) and [PDMP][ZrCl₃ × THF]₂ (8), gave higher activities than the titanium complexes, [PDMP]TiCl₂ (5) and [PDMP][TiCl₃]₂ (6). The bimetallic complexes (6, 8) gave higher activities than the corresponding monometallic complexes (5, 7). The titanium complexes gave polymers with higher molecular weight (M_w) than the zirconium complexes. The molecular weight distribution (M_w/M_n) of the polymers obtained from the pyridine diamide complexes were much broader than that of the normal metallocene catalysts. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3756–3762, 1999     

Thermal properties of poly(ester‐imide)s with C12H24 and C22H44 groups

The thermal properties of poly(4,4′‐phthaloimidobenzoyl‐n‐methyleneoxycarbonyl) with n =12 and 22, abbreviated as PEIM‐12 and PEIM‐22, respectively, have been studied using differential scanning calorimetry (DSC). The heat capacities of the solid states of both polymers were measured and compared to computed heat capacities from approximate vibrational spectra. The deviations from the vibrations‐only heat capacity were used to identify large‐amplitude, conformational motions. The heat capacities of the liquid states were described as linear functions of temperature. They agreed with the liquid heat capacities generated from the ATHAS addition scheme using group contributions derived from polymers containing the same chemical segments as the PEIM‐ns. Knowing the heat capacities for the solid and liquid, the transition parameters could be separated and enthalpies, entropies, and free enthalpies obtained. With these data, the change of the crystallinity with temperature could be computed. In the early stages of solidification both compounds contain significant entropy contributions from conformational ordering of the flexible spacer and little from the rigid, aromatic segments. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 319–328, 2000     

Controlled synthesis of SrCrO4 crystals with different morphologies

Rod‐shape, branch‐shape, bouquet‐shape and claw‐shape SrCrO₄ crystals were synthesized through biomembrane/organic‐addition supramolecular templates. The shapes are mainly changed with variance of the organic reagents and organic membranes. Most of the morphologies haven't been reported in the literature. This method may meet with the requirements to synthesize materials of various morphologies and size by using different supramolecular templates. This paper discusses how to control crystals' growth by supramolecular templates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Donor‐unsupported Phosphanylmethanides Li[CH2PR2] (R = tBu,Ph) – Crystal Structure of Li[CH2PtBu2] Solved by XRPD and DFT‐D Calculations

The solvent‐free methyllithium derivatives Li[CH₂PR₂] (R = tBu, Ph) were prepared via the reaction of CH₃PR₂ with Li[tBu]. It should be noted that the deprotonation of CH₃PtBu₂ with Li[tBu] occurred at 60 °C, whereas Li[CH₂PPh₂] was already formed from CH₃PPh₂ with Li[tBu] at ambient temperature. The structure determination of di‐tert‐butylphosphanylmethyllithium was performed by high resolution X‐ray powder diffraction analysis at different temperatures. This led to two possible structure solutions with similar quality criteria (space groups Iba2 and I2/a). Therefore CASTEP DFT‐D calculations were applied to verify the correct crystal structure. The solid‐state structure of di‐tert‐butylphosphanylmethyllithium consists of alternating edge‐sharing six‐ and four‐membered rings, which form a polymeric, infinite double‐chain along the crystallographic c axis in the monoclinic space group I2/a. Two Li[CH₂PtBu₂] units connected via an inversion center form a six‐membered Li₂C₂P₂ ring in the chair conformation. The nearly flat four‐membered Li₂C₂ ring, is oriented perpendicularly to the twofold axis.     

Analysis and confirmation of synthetic anorexics in adulterated traditional Chinese medicines by high-performance capillary electrophoresis.

Six synthetic anorexics, clobenzorex, diethylpropion, fenfluramine, methamphetamine, phenylpropanolamine and phentermine, which can be found as adulterants in traditional Chinese medicines were assayed simultaneously by high-performance capillary electrophoresis. The electrolyte was a buffer solution containing 120 mM phosphate buffer (NaH2PO4/H3PO4, pH 2.0) and 15% acetonitrile. Applied voltage was 16 kV and temperature was 30 degrees C. Fluoren-2,7-diammonium chloride was used as an internal standard and detector set at 200 nm. The recoveries of the synthetic anorexic adulterants in traditional Chinese medicinal formula using C8-SCX mixed solid-phase extraction were studied. Several traditional Chinese medicinal powders obtained from clinics were also studied by the above HPCE method and confirmed by GC-MS. Clobenzorex, diethylpropion and fenfluramine were found and determine in these samples.     

Effects of UV-B radiation on growth, photosynthesis, UV-B-absorbing compounds and NADP-malic enzyme in bean (Phaseolus vulgaris L.) grown under different nitrogen conditions.

The effects of UV-B radiation on growth, photosynthesis, UV-B-absorbing compounds and NADP-malic enzyme have been examined in different cultivars of Phaseolous vulgaris L. grown under 1 and 12 mM nitrogen. Low nitrogen nutrition reduces chlorophyll and soluble protein contents in the leaves and thus the photosynthesis rate and dry-matter accumulation. Chlorophyll, soluble protein and Rubisco contents and photosynthesis rate are not significantly altered by ambient levels of UV-B radiation (17 microW m-2, 290-320 nm, 4 h/day for one week). Comparative studies show that under high nitrogen, UV-B radiation slightly enhances leaf expansion and dry-matter accumulation in cultivar Pinto, but inhibits these parameters in Vilmorin. These results suggest that the UV-B effect on growth is mediated through leaf expansion, which is particularly sensitive to UV-B, and that Pinto is more tolerant than Vilmorin. The effect of UV-B radiation on UV-B-absorbing compounds and on NADP-malic enzyme (NADP-ME) activity is also examined. Both UV-B radiation and low-nitrogen nutrition enhance the content of UV-B-absorbing compounds, and among the three cultivars used, Pinto exhibits the highest increases and Arroz the lowest. The same trend is observed for the specific activity and content of NADP-ME. On a leaf-area basis, the amount of UV-B-absorbing compounds is highly correlated with the enzyme activity (r2 = 0.83), suggesting that NADP-ME plays a key role in biosynthesis of these compounds. Furthermore, the higher sensitivity of Vilmorin than Pinto to UV-B radiation appears to be related to the activity of NADP-ME and the capacity of the plants to accumulate UV-B-absorbing compounds.     

DSC Analysis of the Induction Period in the Vulcanisation of Rubber Compounds

Vulcanisation of rubber compounds was studied by DSC under isothermal and non-isothermal conditions. The parameters of an Arrhenius-like equation describing the temperature dependence of induction period have been obtained both from isothermal and non-isothermal measurements. A new method for obtaining the kinetic parameters from non-isothermal measurements, based on the dependence of onset temperature of vulcanisation peak on heating rate, is presented. Also, a procedure for the evaluation of temperature difference between the furnace and sample is proposed. It has been shown that the treatment of non-isothermal DSC measurements gives the kinetic parameters free of systematic errors. The new method can also be used for studying other reactions exhibiting the induction period. This revised version was published online in August 2006 with corrections to the Cover Date.     

Low-field magnetoresistance of strongly modulated two-dimensional electron gas

The typical form of the low-field magnetoresistance anomaly induced by a strong one-dimensional periodic modulation of the background potential is described. It is shown that the magnetoresistance peak due to the magnetic breakdown is always followed by a resistance increase at higher magnetic fields, for which οcτ > 1.