三价铬和六价铬对梨形四膜虫生长的影响

本文采用梨形四膜虫S1作为生物体材料,探讨了三价铬和六价铬对细胞生长的影响。实验结果表明Cr(Ⅲ)在10ppm以下,对梨形四膜虫生长有促进作用,但是Cr(Ⅵ)在1ppm以上时对梨形四膜虫的生长即产生抑制作用,我们又观察到Cr(Ⅵ)在10ppm时对梨形四膜虫的生长,开始有强抑制作用,在30小时以后,四膜虫细胞呈现突跃式的增长,我们对此现象作了初步探讨。     

黄县褐煤净化含铬废水的研究

本文主要是研究黄县褐煤净化含铬废水的条件、机理和效果。发现pH<3时,褐煤净化Cr(Ⅵ)的效果较好;pH>4时.净化Cr(Ⅲ)的效果较好。pH值较低时,褐煤对Cr(Ⅵ)的净化有吸附和还原作用。净化方法简易可行。     

Coated wire chromium(III) ion-selective electrode based on azamacrocycles

Tetraazacyclotetradecane, tetratosyltetraaza 12C4, and tritosyltriaza 9C3 have been explored as electroactive materials for preparing coated wire ion-selective electrodes (CWISEs) for Cr(III) ions. The best performance was observed for the membrane comprising electroactive material (tetratosyltetraaza 12C4), plasticizer (dibutyl phthalate), and poly(vinyl chloride) in the optimum ratio 5:60:35 (w/w). Linear Nernstian response for this electrode was obtained over the total Cr(III) concentration range of 1×10^–1 to 1×10^–7 M in 0.05 M NH₄NO₃ medium, with a slope of 20±1 mV per decade change. The working pH range of the electrode was 1.8–5.5. Selectivity coefficients of some mono, divalent, and trivalent metal ions were determined. Analyses of electroplating bath solutions, chromating, and effluent samples have been carried out using this CWISE and the results are found to be comparable with those obtained by using conventional methods or by AAS.     

Microchemical Analysis and Microstructural Development of Cr-Doped Mullites

A characterization study of chromium doped sol–gel mullites (with Cr₂O₃ contents varying between 1 and 9wt.%) by means of electron beam techniques is presented. Scanning and transmission electron microscopy studies gave information about general microstructural features, like grain size and shape, presence of glassy phase in triple grain junctions and segregation of secondary crystalline phases. EDX-TEM measurements reveal an upper solubility of chromium in the mullite lattice of approx. 8wt.% Cr₂O₃. The effect of Cr doping in the microstructural development of these mullites is discussed.     

Further study on a flow injection on-line multiplexed sorption preconcentration coupled with flame atomic absorption spectrometry for trace element determination

A further study on a newly developed flow injection (FI) on-line multiplexed sorption preconcentration (MSP) using a knotted reactor coupled with flame atomic absorption spectrometry (FAAS) was carried out to demonstrate its applicability and limitation for trace element determination. For this purpose, Cr(VI), Cu(II), Ni(II) and Co(II) were selected as the analytes, and detailed comparison was made between the MSP-FAAS and conventional FI on-line sorption preconcentration FAAS in respect to retention efficiency and linear ranges of absorbance versus sample loading flow rate and total preconcentration time. Introduction of an air-flow for removal of the residual solution in the KR after each sub-injection in the MSP procedure played a decisive role in the improvement of retention efficiency. The linearity of absorbance versus sample loading flow rate or total preconcentration time was extended to a more degree for the metal ions with less stability of their PDC (pyrrolidine dithiocarbamate) complexes than those with more stable PDC complexes. It seems that the MSP procedure behaves advantages beyond the inflection points in the diagrams of absorbance versus total preconcentration time and sample loading flow rate obtained by conventional (a single continuous) preconcentration procedure. With a sample loading flow rate of 6.0 ml min⁻¹ and a total preconcentration time of 180 s, the retention efficiencies were increased from 25, 46, 41 and 63% with a single continuous sorption preconcentration to 44, 78, 65 and 75% with a six sub-injection preconcentration procedure for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The detection limits were 0.40, 0.33, 0.31 and 0.26 μg l⁻¹ for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The precision (R.S.D.) for eleven replicate determination of 2 μg l⁻¹ Cr(VI), Co(II) and Ni(II), and 1 μg l⁻¹ Cu(II), was 2.1, 4.1, 2.6 and 1.7%, respectively.     

Towards the total synthesis of tonantzitlolone--preparation of key fragments and the complete carbon backbone

The first synthetic advances towards the novel diterpenoid tonantzitlolone 1 are described. The key steps in the synthesis involve a chromium(II) Reformatsky reaction, a diastereoselective C₁ extension and an expeditious aldol coupling step of two advanced precursors.     

A solid-phase version of the Nozaki-Hiyama allylation of aldehydes with supported allylic bromides

A solid-phase version of the Nozaki-Hiyama allylation of supported allylic bromides with aldehydes is described. α-Methylene γ-butyrolactones 7 can be obtained by cyclization cleavage of the supported intermediate homoallylic alcohols 6.     

A new method for the preparation of N-stabilized allenylidene complexes of chromium and tungsten

Displacement of tetrahydrofuran in [(CO)₅M(THF)] (M=Cr, W) by the anion [CCC(X)Y]⁻ (X=O; NR; Y=NR′₂, Ph) followed by alkylation of the resulting metalate with [R″₃O]BF₄ (R″=Me, Et) offers a convenient and versatile route to π-donor-substituted allenylidene complexes, [(CO)₅MCCC(XR″)Y]. Allenylidene complexes in which the terminal carbon atom of the allenylidene ligand constitutes part of a heterocycle are likewise accessible by this reaction sequence. Reaction of [(CO)₅M(THF)] with Li[CCC(NMe)Ph]⁻ and subsequent protonation of the metalate afford [(CO)₅MCCC(NMeH)Ph] in high yield. As indicated by the spectroscopic data of the compounds and the X-ray analyses of three representative examples, these allenylidene complexes are best described as hybrids of allenylidene and zwitterionic alkynyl complexes with delocalisation of the electron pair at nitrogen towards the metal center. Dimethylamine reacts with the amino(phenyl)allenylidene complex [(CO)₅CrCCC(NMe₂)Ph] (7a) by addition of the amine across the C_αC_β bond to give selectively the E-alkenyl(amino)carbene complex [(CO)₅CrC(NMe₂)CHC(NMe₂)Ph] (12). In contrast, the reaction of dimethylamine with the amino(methoxy)allenylidene complex [(CO)₅CrCCC(NMe₂)OMe] (1a) proceeds by addition of the amine to the C_γ atom and subsequent elimination of methanol to give the substitution product [(CO)₅CrCCC(NMe₂)₂] (13). Triphenylphosphane neither adds to the C_α nor the C_γ atom of 7a but upon irradiation displaces a CO ligand to form a cis-allenylidene(tetracarbonyl)phosphane complex 15.     

Quinolyl-functionalised Cp-chromium polymerisation catalysts: synthesis and crystal structures of alkylation products

The quinolyl-functionalised Cp-chromium(III) complexes 1 and 2, which serve as precursors for highly active olefin polymerisation catalysts, were alkylated with benzylmagnesium chloride. From these reactions, the new metal complexes 4, 5 and 6 were obtained and structurally characterised. The expected alkylchromium compound 4 is formed together with complex 5, where the nucleophile replaced a hydrogen atom at the quinoline substituent. The dinuclear complex 6 is formed by nucleophile addition, rearrangement and dimerisation.     

Determination of Cr (in small quantities) by adsorptive stripping voltammetry: a comparative study of square wave versus differential pulse

The usefulness of an analytical method must be measured according to its practical application possibilities. A comparative study has been carried out here between the SW (working in an open atmosphere) and DP (working with de-aerated solutions) variants of catalytic-stripping adsorptive voltammetry applied to the determination of chromium traces in triethylenetetraminehexaacetic acid (TTHA) medium. In order to optimise the analytical signal, accumulation potential, nitrate ion concentration, pH, and TTHA concentration parameters were evaluated. Four linearity ranges were established within the interval 0.5–2000 nmol L^–1 chromium concentration in the cell, each with the recommended accumulation time. Quality parameters such as repeatability, linear regression, validity limits, precision, and sensitivity were evaluated. The SW variant is significantly advantageous when the chromium concentration in cell is less than 10 nmol L^–1 and even more if analysis time, cost, and being able to work in an open atmosphere are considered. The results are comparable to those obtained using GTAAS. Employing a CRM (tomato leaves), the accuracy is 1–4%. The proposed procedure, using tree leaves as samples, has been successfully tested for the possible monitoring of chromium contamination of the atmosphere.