Determination of cadmium and copper with ET-AAS after electrochemical deposition on a graphite electrode

The electrodeposition of cadmium and copper on a special graphite disk electrode has been performed at controlled potential. The electrode with the deposit has been inserted into the graphite atomizer HGA-400 by an adapted automatic sampler for the final determination by ET-ASS. The sensitivity of determination has been 0.371 (microg l(-1))(-1) for cadmium and 0.025 (microg l(-1))(-1) for copper for 2 min electrodeposition and increased linearly with the time of deposition. The limit of detection (3s(bl)) has been 7.9 ng l(-1) Cd(2+) and 0.11 microg l(-1) Cu(2+) for 2 min deposition and it has been improved with increased time of electrodeposition. The technique has been applied to the determination of both metals in seawater and to speciation in the presence of EDTA complexing agent.     

Study of solvents effect on distribution of configurational and conformational isomers of apo-tirucallol theoretically and experimentally

The adsorption of carbon monoxide on the rutile (1 1 0) and the anatase (1 0 1) surfaces has been investigated by a periodic approach using hybrid-exchange density functional theory; the quantum-mechanical study on the CO adsorption on the anatase surface has been carried out for the first time. The full optimization of the systems has been performed by considering different surface coverages and periodicities. The adsorption energetics have been investigated, on the basis of a recently proposed model, in terms of interaction, distortion and binding energies and the lateral effects have been analyzed using a simple model of nearest and next-nearest neighboring molecules. The experimental adsorbed CO stretching frequencies have been compared with the computed ones obtained by considering the highest investigated periodicity. The Lewis acidity of the two surfaces is comparable and the rutile (1 1 0) acid site seems to be slightly more electrophilic than that of the anatase (1 0 1) one.     

Change in the activity of the proteolytic enzymes of cotton seeds when the plants are affected by wilt

The change in the proteolytic activity of the seeds of the cotton plant varieties Tashkent-1- Tashkent-6, S-4727, and 108-F when the plants are affected by wilt has been studied. A relationship has been established between the decrease in activity for seeds of the Tashkent-1 and Tashkent-6 varieties and the degree of attack by wilt. A hypothesis has been put forward on the existence of variety differences in the response reaction of the cotton plant to the introduction of the pathogen. The appearance of distinctive electrophoretic protein components in the seeds of wilt-affected cotton plants of the Tashkent-1 and Tashkent-6 varieties has been shown. A hypothesis has been made of a possible increase in the amount of proteinase inhibitors in response to the infection of the plants by wilt, a consequence of which is a sharp decrease in proteolytic activity and the appearance of distinctive electrophoretic components.     

Enzyme electrode probes obtained by electropolymerization of monomers with PMS and selected dehydrogenase enzymes

5-methylphenazonium methylsulphate, (commonly named phenazine methosulphate, PMS) mediated electroxidation of beta-nicotinamide adenine dinucleotide (phosphate), reduced form, (NAD(P)h), on platinum, gold and carbon electrodes has been studied by electropolymerization of 1,2-, 1,3-, 1,4-diaminobenzene (DAB), pyrrole-2-carboxylic acid (PY-2-COOH) and 4,4'-dihydroxybenzophenone (DHB) in presence of PMS using cyclic voltammetry. The electroxidation of ascorbic acid has been evaluated on the electrodes electropolymerized in absence and in presence of PMS. The same experiments have been carried out with NAD(P)H in solution. Results showed that the NAD(P)H is oxidised by PMS coimmobilized with the polymer film on the electrode surface. NAD(P)H has been measured in the range 10(-6)-10(-2)mol l(-1) with a detection limit of 5 x 10(-7) mol 1(-1). Amperometric measurements of NAD(P)H have been carried out at -0.10 V and the efficiency of different elecrodes based on different materials has been studied. The electropolymerization has been also carried out in presence of PMS and selected dehydrogenase enzymes. The activity of these enzymes has been tested amperometrically at -0.1 V. Enzyme substrates such as glucose, lactate and glutamate have been measured in the range 5 x 10(-6)-1 x 10(-2) mol 1(-1) with a detection limit 1 x 10(-6) mol 1(-1). Also the stability of these probes during time has been evaluated.     

Development and validation of a high-performance liquid chromatography method for quantification of egonol and homoegonol in Styrax species

Styrax camporum Pohl, known in Brazil as 'estoraque do campo' or 'cuia de brejo', has been used in the treatment of gastrointestinal diseases. The therapeutic action of S. camporum has been attributed to the ethyl acetate fraction, although the chemical composition of this fraction has not yet been analyzed. In this study, a high-performance liquid chromatography photodiode array detection (HPLC-PAD) method for analysis of Brazilian Styrax species has been developed. The compounds egonol (1) and homoegonol (2) were found to be present in all the samples investigated by HPLC. These compounds were isolated by open column chromatography followed by preparative TLC, and were identified by 1H NMR. Compounds 1 and 2 were thus proposed as phytochemical markers for Styrax, owing to their biological properties and presence in other Styrax species. The developed method has been validated and successfully applied for quantification of 1 and 2 in S. camporum dried leaves and crude ethanolic extracts from S. ferrugineus and S. pohlii aerial parts.     

Reaction of diphenylphosphine oxide with a 10-methylacridinium salt. Reversible formation of a P?C covalent bond

Diphenylphosphine oxide ( 1 ′) reacts reversibly with a 10-methylacridinium salt ( 2 ) in acetonitrile at 20°C to equilibrate with a new salt 3 formed by the addition of 1 ′ to the cation of 2 . The forward reaction in this equilibrium proceeds via nucleophilic attack by the phosphorus atom of diphenylphosphinous acid ( 1 ), the trivalent tautomer of 1 ′, upon the 9-carbon atom of the cation of 2 , forming a phosphorus–carbon covalent bond. The equilibrium constant has been determined by UV-vis and ¹H NMR spectroscopy as well as by HPLC analysis. The reaction has been analyzed kinetically, and the results have been compared with those obtained in the similar reaction of an alkyl ester of 1 , the diphenylphosphinite ( 5 ), with 2 that gives the phosphonium salt 6 . It is suggested that 6 is much more stable than 3 . The equilibrium constant for the tautomerism between 1 ′ and 1 has also been estimated. © 1995 John Wiley & Sons, Inc.     

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.     

ZSM-5沸石上Brönsted酸的红外光谱测定法及改性ZSM-5沸石的表面酸性研究

研究各种 ZSM-5沸石样品的红外光谱发现: 在1875和2000 cm~(-1)附近有两个强红外吸收谱带, 两个谱带吸光度的比值是个特征值。本文提出了以2000 cm~(-1)谱带为“内标”, 用相对吸光度的办法处理ZSM-5沸石的红外光谱, 测定了各种改性ZSM-5样品的Brönsted酸, 并同电位滴定法所测得的Brönsted 酸浓度和异丙苯裂解活性分别关联, 都有较好的对应关系。文中以实验为依据讨论了1875和2000 cm~(-1)谱带的归属, 并根据Beer-Lambert定律, 推导出了相对吸光度与浓度的关系, 从而确立了ZSM-5沸石上红外光谱定量处理方法的理论基础。     

Molecular dynamics simulation of the 1:1 enzyme-ligand complex between porcine pancreatic elastase and acetyl-alanine-proline-alanine

A 31.5 picosecond (ps) MD calculation has been completed for the 1:1 enzyme-ligand complex between porcine pancreatic elastase (PPE) and acetyl-alanine-proline-alanine (APA). The 1:2 complex studied crystallographically at product saturation conditions precludes the study of a 1:1 complex (PPE and APA1); this objective has been achieved by computational methods described here. The acetyl group of the ligand was found to occupy two neighboring sites, one within the primary specificity site and the other out into solution. The primary change of the ligand structure is ψ₁ torsion angle being 171.5°. Supported by an interactive graphic display, the dynamical fluctuations of a smaller ligand compared with the width of the active site as PPE were observed by the MD simulation, although the complex has not been detected by any spectroscopic method.     

1,1'-Binaphthyl-substituted macrocycles as receptors for saccharide recognition

The preparation of receptors for saccharide recognition in a natural environment has been an unmet goal for a long time. We present herein the synthesis and binding properties of (R,S)-1,1'-binaphthyl-substituted macrocycles as receptors for saccharide recognition in water/acetonitrile (1:1) and in DMSO. Porphyrin and metalloporphyrin macrocycles with two to four 1,1'-binaphthyl substituents and multiple hydroxy groups generate a binding site for saccharides that incorporates hydrogen-bonding hydroxy groups together with the aromatic hydrophobic pocket. The specificity for di- and trisaccharides is governed by the cavity size. The mechanism of binding has been studied by 1H NMR spectroscopy and the role of H-bonding and CH-pi interactions has been evaluated; the ability to bind saccharides has been demonstrated by the surface plasmon resonance (SPR) technique. The application of these macrocyclic receptors to sensor development is also presented.     

Synthetic transformation of ptychantin into forskolin and 1,9-dideoxyforskolin

Forskolin (1), a highly oxygenated labdane diterpenoid and an activator of adenylate cyclase, has been synthesized in 12 steps and 12% overall yield from ptychantin A (4), which has been isolated from liverwort Ptychanthus striatus in good yield. The 1alpha-hydroxy group was furnished by stereoselective reduction of the corresponding carbonyl group by sodium in t-BuOH. The 9alpha-hydroxy group was introduced stereoselectively by epoxidation of delta(9.11)-enolether. 1,9-Dideoxyforskolin (2), an inhibitor of glucose transporter, has been synthesized in 8 steps and 37% overall yield. The hydroxy group at C-1 was removed by solid-state thicarbonylimidazolation and subsequent radical cleavage.     

Unusually high pyramidal geometry of the bicyclic amide nitrogen in a complex 7-azabicyclo[2.2.1]heptane derivative: Theoretical analysis using a bottom-up strategy

The high pyramidalization of the bicyclic amide nitrogen found in the crystal structure of a dipeptide incorporating (1S,2S,4R)-N-benzoyl-2-phenyl-7-azabicyclo[2.2.1]heptane-1-carboxylic acid has been investigated using quantum mechanical calculations. More specifically, a bottom-up strategy based on the study of model molecules of progressive complexity has been used. First, an appropriate quantum mechanical method has been selected by examining the distortion of the amide bond in three simple model molecules. Next, the amide distortion induced by the norbornane ring has been evaluated by considering three different 7-azabicyclo[2.2.1]heptane amides. After this, the suitability of quantum mechanical calculations to predict the effect of the substituents on the pyramidalization of the bicyclic amide nitrogen has been investigated by comparing experimental and theoretical parameters for a number of compounds. Finally, the factors responsible for amide distortion in the (1S,2S,4R)-N-benzoyl-2-phenyl-7-azabicyclo[2.2.1]heptane-1-carboxylic acid derivative have been elucidated using a hierarchical approach. For this purpose, several derivatives were generated by removing or modifying the substituents attached to the 7-azanorbornane system. Results have been discussed in terms of intramolecular specific interactions.     

Atranes

The kinetics of the hydrolysis of 15 1-alkyl-, 1-alkoxy- and 1-hydrosilatranes in an aqueous medium has been studied. The hydrolysis reaction is described by a first-order kinetic equation. 1-Hydrosilatrane is hydrolyzed most readily and 1-isopropyl- and 1-tert-butoxysilatranes with the greatest difficulty. A correlation has been drawn up of the logarithms of the rate constants of the hydrolysis of the silatranes and the ^* constants of the substituents, the influence of the latter on the reaction has been discussed, and a scheme for its mechanism has been put forward.For part XVII, see [1].     

Palladium η3-allyl complex with sorbic acid: Kinetics and mechanism of protodemetalation in aqueous solutions

The allyl complex di-μ-chloro-bis[(1,2,3-η)-1-carboxy-3-(1-hydroxyethyl)allyl]dipalladium (which is a hydroxyl-containing palladium η³-allyl complex based on sorbic acid) has been synthesized from trans,trans-2,4-hexadienic (sorbic) acid and Na₂PdCl₄ in an aqueous solution. The complex has been isolated from the reaction solution and has been characterized by IR, ¹H NMR, and ¹³C NMR spectroscopy. Its composition has been determined by elemental analysis. The protodemetalation kinetics of the complex in aqueous solutions has been studied. The rate of this reaction obeys a second-order equation, first-order with respect to each reactant. A reaction mechanism has been derived from protodemetalation kinetics and data characterizing the state of the reactants.     

New fluorenyl-substituted ditopic dioxotetraamine ligands and their copper(II) complexes--synthesis, crystal structure, magnetic properties and solution behavior

A new fluorenyl-substituted dioxotetraamine salicylaldehyde Schiff-base ligand (L1) has been synthesized by the non-template 1 + 2 condensation of ligand 6-(9-fluorenyl)-1,4,8,11-tetraazaundecane-5,7-dione (L) with salicylaldehyde. From reduction of L1 with an excess of NaBH4, a ditopic dioxotetraamine ligand (L2) has been obtained. The copper(II) complex of L1 has been synthesized and its properties were examined by ES-MS and variable-temperature magnetic susceptibility as well as its crystal structure being determined. Detailed studies have been made on solution chemistry of Cu(II) complex of L2 by pH-potentiometric and fluorometric titration.     

Inhibition Effect of {Cationic Surfactant-Ascorbic Acid} Premicellar Aggregation on the Rate of Hexacyanoferrate(III) Oxidation of Ascorbic Acid: A Kinetic Study

The kinetics of oxidation of ascorbic acid by acidic hexacyanoferrate(III) have been investigated in presence of cationic surfactant viz. cetyltrimethylammonium bromide (CTAB). An inhibition effect of CTAB (below its critical micelle concentration) on the rate of oxidation has been observed. The spectrophotometric and kinetic data support a 1:1 premicellar association between substrate and surfactant. A mechanism has been proposed and a rate law consistent with kinetic results has been derived.     

Synthesis,characterization and catalytic activity of Rh (PPh3)2 (en)Cl complex

Ethylenediamine bis(triphenylphosphine) monochlororhodium has been prepared by the interaction of Wilkinson's catalyst and ethylenediamine in benzene. The complex has been isolated and characterized by conventional and spectroscopic methods. The catalytic activity of the complex was investigated for the hydrogenation of 1-octene as a model reaction at a hydrogen pressure of 1 atmosphere (101 kPa) using methanol as a solvent. The influence of various factors such as catalyst, substrate concentrations and temperature have been studied. The hydrido complex has been identified as an intermediate product by IR and NMR studies. The experimental data are in accordance with a rate expression of the form: .     

Studies on Biologically Potent Tetraazamacrocyclic Complexes of Bivalent Tin

Fourteen- to eighteen-membered tetraamide macrocyclic ligands N 4 L 1 -N 4 L 4 have been prepared by the condensation of 1,2-diaminoethane or 1,3-diaminopropane with malonic or succinic acid in the presence of condensing reagents dicyclohexylcarbodiimide and 4-dimethylaminopyridine. On reduction, these macrocyclic ligands give a new series of tetraazamacrocycles MacL 1 -MacL 4 which form complexes with tin(II) chloride. The ligands and their complexes were characterized by elemental analyses, molecular weight determinations, infrared and 1 H NMR spectral studies. The hexacoordinated state for tin has been confirmed by spectral studies. An octahedral geometry for these complexes has been proposed as the binding sites are the nitrogen atoms of the macrocycles. On the basis of the chemical composition the representation of the complexes as [Sn(MacL n )Cl 2 ] (n = 1-4) has been established. The ligands and their complexes also have been screened for their antifungal and antibacterial activities and the findings have been reported and explained.     

硝酸铈(Ⅳ)与四氧二氮环醚配合物

本文报道通过中间配合物Ce(OPPh₃)₂(NO₃)₄与1,7,10,16-四氧-4,13-二氮杂环十八烷作用制得一组成为Ce(C₁₃H₂₆N₂O₄)(NO₃)₄·2.5(CH₃COCH₃)的黄色固体配合物。该配合物在空气中稳定,在大多数有机溶剂中不溶解,但可溶于DMSO中。运用电导、波谱技术对该配合物的性质进行了研究。     

Adsorption Behavior and Inhibition Corrosion Effect of Sodium Carboxymethyl Cellulose on Mild Steel in Acidic Medium

The effect of sodium carboxymethyl cellulose (Na-CMC) on the corrosion behavior of mild steel in 1.0 mol·L-1 HCl solution has been investigated by using weight loss (WL) measurement, potentiodynamic polarization, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) methods. These results showed that the inhibition efficiency of Na-CMC increased with increasing the inhibitor concentration. Potentiodynamic polarization studies revealed that the Na-CMC was a mixed type inhibitor in 1.0 mol·L-1 HCl. The adsorption of the inhibitor on mild steel surface has been found to obey the Langmuir isotherm. The effect of temperature on the corrosion behavior of mild steel in 1.0 mol·L-1 HCl with addition of 0.04% of Na-CMC has been studied in the temperature range of 298-328 K. The associated apparent activation energy (E*a ) of corrosion reaction has been determined. Scanning electron microscopy (SEM) has been applied to investigate the surface morphology of mild steel in the absence and presence of the inhibitor molecules.