Copper–mercury film electrode for cathodic stripping voltammetric determination of Se(IV)

The copper-mercury film electrode has been suggested for the determination of Se(IV) in a wide range of concentration from 1x10(-9) to 1x10(-6) mol L(-1)by square-wave cathodic stripping voltammetry. Insufficient reproducibility and sensitivity of the mercury film electrode have been overcome by using copper(II) ions during the plating procedure. Copper(II) has been found to be reduced and form a reproducible copper-mercury film on a glassy carbon electrode surface. The plating potential and time, the concentration of copper(II) and the concentration of the supporting electrolyte have been optimised. Microscopy has been used for a study of the morphology of the copper-mercury film. It has been found that it is the same as for the mercury one. The preconcentration step consists in electrodeposition of copper selenide on the copper-mercury film. The relative standard deviation is 4.3% for 1x10(-6) mol L(-1) of Se(IV). The limit of detection is 8x10(-10) mol L(-1) for 5 min of accumulation.     

Studies on the biosynthesis of taxol. Synthesis Of taxa-4(20), 11(12)-diene-2alpha,5alpha-diol

The synthesis of taxa-4(20),11(12)-diene-2alpha,5alpha-diol is described. An improved procedure for the intramolecular Diels-Alder cycloaddition previously reported in our synthesis of taxa-4(5), 11(12)-diene has been utilized to prepare a taxoid with oxygenation in the B and C rings. It has been established previously that taxa-4(20),11(12)-dien-5alpha-ol is the first oxygenated intermediate on the biosynthetic pathway to Taxol. Taxa-4(20), 11(12)-diene-2alpha,5alpha-diol (5), which has been observed in a biosynthetic conversion, is a potential candidate as the second oxygenated intermediate on the Taxol biosynthetic pathway, has been prepared to probe the intermediacy of this substance.     

Study on Speciation of Pr(III) in Human Blood Plasma by Computer Simulation

Biological effects of metal are controlled by its in vivo speciation l'2. It is not possible todetermine in vivo speciation of metals with analytical methods so far. The lowmolecular-weight complex distribution of biometal ions in blood plasma was studied bycomputer simulation'. Soluble species of rare earth were also reported 2'3. However,insoluble species of rare earth in blood plasma have not been studied, it is the aim of thispaper to study insoluble species by computer simulation.We impr…     

The Spectrophotometric Determination of Sc in Eriochrome Canine R(Chrome azurol s)- Phosphatidl Choline System

Abstract

Eriochrome cyanine R(chrome azurol S) is used as a color reagent to determine Sc in the presence of phosphatidyl choline, σ = 3.7 × 10⁴ (4.5 × 10⁴). This method has been connected to extraction separation to determine Sc in the presence of rare earth elements, and good results have been obtained.

Phosphatidyl choline(PC) is a biochemical reagent, which can be used as a surfactant. It has been reported that chrome azurol S(CAS) can be used to determine Be in the presence of PC¹ but it has not been reported that eriochrome cyanine R(ECR) and CAS can be used to determine Sc in the presence of PC. This paper has put forward a method by which Sc can be determined. ECR (CAB) has been used as a color reagent and PC as a surfactant. Conditional experiments have been made and this method has been connected to extraction separation. Tributyl phosphate (TBP) extracts Sc from rare earth elements to make a determination and good results have been obtained.     

一系列多核Mo(W)-Cu(Ag)-S簇合物的低热固相合成、成簇规律和机理的研究

本文报道了一系列多核Mo(W)-Cu(Ag)-S族合物的低热固相合成, 发现硫代钼(钨)酸铵与铜(银)的成簇规律主要与固相反应温度密切相关, 提出了四核至七核Mo(W)-Cu(Ag)-S簇合物的可能成簇机理。     

Comparative vapour phase FTIR spectra and vibrational assignment of manganese pentacarbonyls derivatives of the type XMn(CO)5: (where X=Br, Cl, I, H, D, CH3, CD3, CF3)

The infrared spectra of pure Mn(CO)(5)X in the region 4000-400 cm(-1) has been obtained in the vapour phase. The observed spectrum has been analyzed to distinguish the fundamental frequencies, the rotational-vibrational and structure, and overtone and combination frequencies. The assignment of the observed vapour phase frequencies to the fundamental modes of vibration has been made on C(4V) symmetry. The weak peaks due to XMn(CO)(4)((13)CO) molecules have been measured and assigned for all molecules. This study provides a comprehensive comparison of these compounds, with all of these data the assignment of frequencies is reviewed and a set of quite unambiguous assignments made. The significant finding in this regards are that, it is not necessary to assume lower than C(4V) symmetry for XMn(CO)(5) as has been done in previous consideration of some infrared spectrum of these compounds.     

Chromatographic behaviour of 47 metal ions on titanium(IV) arsenate papers

Titanium arsenate papers with As/Ti ratios 0.2-2.2 have been prepared and 47 metal ions chromatographed on these papers in 10(-5)-4M nitric acid. The effect of pH and of the Ti/As ratio on the R(f) values has been studied. A new quantity R(i) (R(i) = R(f) on untreated papers minus R(f) on treated papers) has been defined. The effect of the concentration of the loading reagents on the Ti/As ratio of the ion-exchanger precipitated on the papers has been determined Contrary to Alberti, it is shown that Lederer's equation is obeyed by titanium arsenate papers in the sodium form if the activity of Na(+) ions is considered instead of their concentration. It has also been demonstrated that the selectivity sequence for cations on titanium arsenate papers is not the same as that on titanium arsenate columns.     

The preparation and properties of the acetate complex of trivalent cobalt

A reasonably stable solution of the cobalt(III) acetate complex in glacial acetic acid, containing no water or cobalt(II), has been prepared by the anodic oxidation of the corresponding cobalt(II) acetate solutions at a platinum electrode in a closed system. Cobalt(III) acetate has also been electrolytically prepared without the addition of sodium acetate. Various materials have been tested as membranes because cellophane, which is usually used, has too high electric resistance and too low mechanical strength. The concentration of water in cobalt(III) acetate solutions has been determined by dielectric constant measurements and it has been found that the cobalt(III) acetate stability is almost independent of the water concentration within the range of 0 to 2% of water. In the closed system, the current efficiency was in the range of 60 to 70%; the best reproducibility was obtained using a porous glass membrane.     

Chiral discrimination of cryptochiral saturated quaternary and tertiary hydrocarbons by asymmetric autocatalysis

Chiral discrimination of saturated hydrocarbons has been very difficult to establish, or has not been possible at all. The first chiral discrimination of cryptochiral 5-ethyl-5-propylundecane 1, that is, (n-butyl)ethyl(n-hexyl)(n-propyl)methane, a chiral saturated quaternary hydrocarbon, which is known to exhibit practically no detectable value of optical rotation between 280 and 580 nm, has been accomplished by asymmetric autocatalysis of pyrimidyl alkanol. The absolute configuration of 1 has been determined. In the presence of (R)- or (S)-1, the reaction between pyrimidine-5-carbaldehyde and diisopropylzinc affords (S)- and (R)-pyrimidyl alkanol with 91-97% ee, respectively. Thus, asymmetric autocatalysis serves as a powerful tool for the chiral discrimination of saturated hydrocarbons.     

Toxicity of cadmium species on luminescent bacteria

The toxicity of cadmium compounds against luminescent bacteria has been measured using the Microtox(R) toxicity bioassay and has been related to the cadmium species. Since the Microtox(R) test is carried out in NaCl (2%) and cadmium forms stable chloro complexes, NaNO(3) and NaClO(4) have been tested successfully as alternative to sodium chloride to provide the adequate osmotic protection of the bacteria. The influence of medium and ionic strength as well as different exposure times on EC(50) values has been evaluated.     

Biophysical,spectroscopic and biochemical investigation of DNA–Cu(II)-GSH interactions

The interaction of DNA with Copper(II)-Glutathione (CuGSH) has been investigated by various biophysical methods. The interaction ratio of DNA and Copper(II)-Glutathione in solution phase has been determined spectrophotometrically and found to be 0.25. EPR spectroscopy and UV–Vis findings suggest that Cu(II)-Glutathione neither bound to the DNA bases covalently nor intercalated, this has further been substantiated by the determination of intrinsic binding constant (2.1 × 10²). Viscometric measurements also support this type of binding to DNA by Cu(II)-Glutathione. EPR studies and visible d–d spectra of CuGSH after interaction with DNA, suggested that Copper remained in the Copper(II) state. DNA conformations after interaction with Cu(II)-Glutathione has been determined spectroscopically. Circular dichroism studies revealed that the B conformation of DNA is changed to A after interaction with Cu(II)-Glutathione. This has further been substantiated by thin film IR (Infrared) studies.     

In-situ heating study on the structural change of surfactant-templated germanium oxide mesostructure

Mesostructured germanium oxide has been well-synthesized by using a surfactant-templated approach under basic hydrothermal conditions. The cationic surfactant cetyltrimethylammonium bromide (CTAB) has formed nanotubes with uniform diameter of about 3.2 nm. Blanket-like morphology of the as-prepared sample has been observed with transmission electron microscopy (TEM). High-resolution TEM image reveals that the nanotubes are connected with inorganic germanium oxide and have self-assembled into periodic mesostructure. In-situ heating X-ray diffraction (XRD) patterns confirm that the germanium oxide is in amorphous phase in the temperature range from room temperature (RT) to 700 degrees C. In-situ heating small-angle X-ray scattering (SAXS) presents the mesostructural change with temperature. The local atomic structures around germanium atom have been obtained with in-situ heating X-ray adsorption fine structure (XAFS) techniques. The stability of this mesostructure has been determined to be correlated with the cationic surfactant CTAB. The structural evolution from the GeO 2/NaOH aqueous solution, the as-prepared sample to the sample heated at 700 degrees C, has been described, and the formation mechanism of mesostructured germanium oxide has been discussed.     

Spectroscopic and thermodynamic study of charge transfer interaction between vitamin B6 and p-chloranil in aqueous ethanol mixtures of varying composition

Charge transfer complexes of 1:1 stoichiometry have been found to form between vitamin B(6) (pyridoxine hydrochloride) and a series of electron acceptors including p-chloranil. Since vitamin B(6) is soluble in water while the electron acceptors are insoluble in water but soluble in ethanol, the medium chosen for study is water-ethanol mixture. From the trends in the CT absorption bands the vertical ionization potential of vitamin B(6) has been determined to be 8.12 eV. The enthalpy and entropy of formation of the complex between p-chloranil and vitamin B(6) have been determined by estimating the formation constant (K) spectroscopically at four different temperatures in 75% ethanol-water mixture. Again, the magnitude of K has been found to decrease noticeably with decrease in dielectric constant of the medium (as the percentage of ethanol in the aqueous-ethanol mixture is increased). A plausible explanation for this has been given in terms of hydrolysis of pyridoxine hydrochloride.     

Titrimetric determination of vanadium(IV) with cerium (IV)sulphate at room temperature using ferroin as indicator

A procedure has been developed for the visual titrimetric determination of vanadium(IV) with cerium(IV) sulphate, using ferroin is redox indicator. The method has been extended to the determination of iron(II) and vanadium(IV) in mixtures.     

Instabilities of the symmetry-adapted restricted-Hartree–Fock ground state in infinite polyenes. II. Nonsinglet instabilities

The stability of the possible ground states of an infinite linear equidistant polyene model has been discussed in the PPP approximation of the unrestricted-Hartree–Fock (UHF ) method. The emphasis has been placed upon the investigation of nonsinglet (triplet) instabilities: the spin-density waves (SDW 's) and the spin-bond-order alternation waves (SBAW 's). For physically realistic parameter sets the SDW ground state of the infinite linear equidistant polyene has been shown to be lowest in energy. Whereas the symmetry-adapted restricted HF (RHF ) solution (SAS ) has been shown to be unstable to the formation of SDW 's and SBAW 's for all investigated parametrizations, the bond-order alternation wave (BAW ) solution has been found to be unstable to the formation of SDW 's, but stable to the formation of SBAW 's; in fact, the BAW 's and the SBAW 's have been shown to yield identical gap widths and ground-state energies (at least in the PPP method). It has been shown that there exist such sets of semiempirical parameters for which the charge-density wave (CDW ) ground state is nonsinglet stable irrespective of the existence of an energetically advantageous SDW solution for the same parameter set.     

Radical polymerization as an indicator reaction for determination of organic compounds

Polymerization of methyl methacrylate (MMA) and 4-vinylpyridine (VP) has been carried out in an aqueous solution in the presence of the initiating system persulfate-tetramethylethylenediamine. The reaction rate has been monitored by measuring the light absorbance of the suspension of the resulting polymer. The effect of 26 model organic compounds on the polymerization rate has been studied. It has been shown that the VP polymerization is inhibited by a smaller number compounds (9 compounds) than the MMA polymerization (22 compounds), which indicates that the former reaction has better selectivity, whereas the determination of model compounds using the MMA polymerization reaction is more sensitive. This is explained by the lower chain growth rate constant for VP vs. MMA and different stationary concentrations of radicals in the systems. The use of these indicator polymerization reactions makes it possible to distinguish some closely related compounds, e.g., 1,4-benzoquinone and 9,10-anthraquinone (MMA reaction) or dinitrophenol and 4-nitrophenol or phenol (VP reaction). Determination of ascorbic acid in a pharmaceutical formulation has been carried out.     

A new chemiluminescence system for determination of cobalt

The chemiluminescence of the reaction of tartaric acid with hydrogen peroxide in the presence of Co(II) in alkaline buffer media has been examined. The maximum emission wavelength is 460 nm. The kinetic curve of the chemiluminescence system has been modelled with a computer, and the reaction conditions have been optimized. Foreign ions, such as Fe(II), Cr(III) and Mn(II), interfere when present in more than 10-fold ratio to Co(II), but several ions can be tolerated when present in higher ratios to Co(II). The concentration range of linear response is from 3.5 x 10(-9) to 2.0 x 10(-6) g/ml, and the detection limit is 4 x 10(-11) g/ml. The procedure has been satisfactorily applied to determine trace cobalt in human blood serum.     

Cl/GaAs(111)表面近边X射线吸收精细结构的多重散射研究

利用多重散射团簇方法（MSC）计算了Cl/GaAs(111)吸附表面的Cl原子k边X射线吸收精细结构谱（NEXAFS）.阐明了NEXAFS谱中各个弱结构的物理起源.根据模型计算的结果与实验比较,求得吸附在顶位的氯原子和最近邻的镓原子的键长为（0.213±0.005）nm.这个结果在0.005 nm的误差范围内将广延X射线吸收精细结构（EXFAS）实验谱的Fourier变换结果（0.217 nm）和Slab模型计算的结果（0.208 nm）合理地联系起来.此外,MSC计算求得衬底表面层Ga－As键长为（0.235±0.005）nm,证实Cl吸附引起GaAs(111)表面驰豫.     

焦磷酸盐溶液中铜电沉积过程 Ⅱ. 用旋转电极的研究

焦磷酸铜络合物还原过程中要经过一价铜这个中间产物在一些文献中都假设过。这个问题不仅是有兴趣的理论问题,而且也很有实际价值。因为在工业电镀中经常出现的所谓“铜粉”,常常影响镀层的质量。简单的Cu~(2+)离子在氧化物溶液中进行阴极还原时,曾经用旋转圆环-圆盘电极(RRDE)的方法实验证实了一价铜中间产物的存在。但是在铜以络离子存在时,尤其是在过剩的焦磷酸离子存在下,使得还原在较负的电位下进行。这时是否有一价铜中间产物,尚未见到RRDE的研究。用RRDE研究络离子还原的工作还很少。可是这一有力方法的应用将会揭示许多一般方     

Measurement of absolute absorption cross sections for nitrous acid (HONO) in the near-infrared region by the continuous wave cavity ring-down spectroscopy (cw-CRDS) technique coupled to laser photolysis

Absolute absorption cross sections for selected lines of the OH stretch overtone 2ν(1) of the cis-isomer of nitrous acid HONO have been measured in the range 6623.6-6645.6 cm(-1) using the continuous wave cavity ring-down spectroscopy (cw-CRDS) technique. HONO has been generated by two different, complementary methods: in the first method, HONO has been produced by pulsed photolysis of H(2)O(2)/NO mixture at 248 nm, and in the second method HONO has been produced in a continuous manner by flowing humidified N(2) over 5.2 M HCl and 0.5 M NaNO(2) solutions. Laser photolysis synchronized with the cw-CRDS technique has been used to measure the absorption spectrum of HONO produced in the first method, and a simple cw-CRDS technique has been used in the second method. The first method, very time-consuming, allows for an absolute calibration of the absorption spectrum by comparison with the well-known HO(2) absorption cross section, while the second method is much faster and leads to a better signal-to-noise ratio. The strongest line in this wavelength range has been found at 6642.51 cm(-1) with σ = (5.8 ± 2.2) × 10(-21) cm(2).