Determination of Pb(II) and Cu(II) by Electrothermal Atomic Absorption Spectrometry after Preconcentration by a Schiff Base Adsorbed on Surfactant Coated Alumina

1,2-Bis（salicylidenamino）ethane loaded onto sodium dodecyl sulfate-coated alumina was used as a new chelating sorbent for the preconcentration of traces of Pb（Ⅱ） and Cu（Ⅱ） prior to atomic absorption spectrometric determination. The influence of pH, flow rates of sample and eluent solutions, and foreign ions on the recovery of Pb（Ⅱ） and Cu（Ⅱ） by this sorbent has been studied. The retained ions were eluted with 4 mol·L nitric acid and determined by electrothermal atomic absorption spectrometry （ETAAS）. The data of limit of detection （3σ） for Pb（Ⅱ） and Cu（Ⅱ） were found to be 8.57 and 2.69 ng·L^-1 respectively, while the enrichment factor for both ions was 100. The proposed method was successfully applied to determination of lead and copper in different water samples.     

EFFECT OF WATER ON THE OXIDATION OF METHANOL OVER ELECTROLYTIC SILVER

The mechanism of methanol adsorption induced by oxygen and the effect of water on the methanol oxidation on electrolytic silver have been studied by ultra-high vacuum temperature programmed reaction spectroscopy(TPRS), transient response method and isotopic exchange experiment. It has been found that oxygen adsorbed on silver can greatly promote methanol adsorption and can also react with methanol to produce water. Experimental results show that oxygen in the water comes from the adsorbed oxygen and hydrogen from the methyl and the hydroxyl in methanol. It has also been found that there exists competitive adsorption between water and oxygen on silver and water can increase the selectivity of methanol oxidation to formaldehyde. This result is consistent with the catalytic activities.     

Use of 2-(tert-butoxy)-N-(3-carbamothioylphenyl)acetamide and graphene oxide for separation and preconcentration of Fe(Ⅲ),Ni(Ⅱ),Cu(Ⅱ) and Zn(Ⅱ) ions in different samples

A simple and selective method using a column packed with graphene oxide(GO) as a solid phase extractant has been developed for the multi-element preconcentration of Fe(Ⅲ),Ni(Ⅱ),Cu(Ⅱ) and Zn(Ⅱ)ions prior to flame atomic absorption spectrometric determinations.The method is based on the sorption of mentioned ions on synthesized GO using 2-(tert-butoxy)-N-(3-carbamothioylphenyl)acetamide as a chelating agent.Several parameters on the extraction and complex formation were optimized.Under the optimized conditions(pH 6,flow rate 9 mL/min),metal ions were retained on the column,then quantitatively eluted by HNO3solution(5 mL,3.0 mol/L).The preconcentration factor was calculated as250.The detection limits for the analyte ions of interest were found in the range of 0.11 ng/mL(Ni2+) to0.63 ng/mL(Cu2+).The column packed with GO was adequate for metal ions separation in matrixes containing alkali,alkaline earth,transition and heavy metal ions.     

SPECTROFLUORIMETRIC DETERMINATION OF GERMANIUM WITH MORIN IN WATER AND HEALTH DRINK

A highly sensitive and fairly selective spectrofluorimetric method has been developed for the determination of germanium with morin in tap water and health drink. The fluorescent reaction and optimal conditions of germanium with morin in phosphoric acid medium were studied. The detection limits of germanium in tap water and health drink were found to be 0.2 and 0.7μd/L respectively.     

SYNTHESIS OF MESO-TETRA (4-METHOXYPHENYL-3-SULFONATE) PORPHINE AND SPECTROPHOTOMETRIC STUDY OF COLOUR REACTION WITH COPPER

In this paper meso-tetra (4-methoxyphenyl-3-sulpho) Porphine (TMPPS_4) was synthesized and its colour reaction with copper was studied. It was found to be a highly sensitive and highly selective reagent for the direct spectrophotometric determination of ultramicro amount of copper. The apparent molar absorptivity of the complex is 3.72×10~5L/mol·cm. Beer's law is obeyed for Cu(Ⅱ)of 0～1.4μg/10ml. The interference of 21 different ions and 6 kinds of salts were examined and found to be minimal. The complex formation of Cu(Ⅱ) with TMPPS_4 is generally slow at room temperature<<25℃>, but the reaction can be accelerated in the presence of NH_2OH·>HCl and completed within 5min. At PH 5.2 the Soret band of TMPPS_4 overlaps almost completetely with that of the complex. Therefore, the complex formation is taken to completion at this PH. Then the Soret band of TMPPS_4 shifted away from that of the complex by acidification.This simple and rapid method has been successfully applied to the direct determination of Cu in Al-alloys, industrial water, foods and human hair.     

Norvancomycin-capped silver nanoparticles: Synthesis and antibacterial activities against E. coli

The synthesis of norvancomycin (NVan)-capped silver nanoparticles (Ag@NVan) and their notable in vitro antibacterial activities against E. coli, a Gram-negative bacterial strain (GNB), are reported here. Mercaptoacetic acid-stabilized spherical silver nanoparticles with a diameter of 16±4 nm are prepared by a simple chemical reaction. The formation process of the silver nanoparticles is investigated by UV-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM). NVan is then grafted to the terminal carboxyl of the mercaptoacetic acid in the presence of N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDAC). The TEM images of single bacteria treated with Ag@NVan show that plenty of Ag@NVan aggregate in the cell wall of E. coli. A possible antibacterial mechanism is proposed that silver nanoparticles may help destroy the stability of the outer membrane of E. coli, which makes NVan easier to bind to the nether part of the peptidoglycan structure. The antibacterial activities of silver nanoparticles on their own, together with the rigid polyvalent interaction between Ag@NVan and cell wall, enables Ag@NVan to be an effective inhibitor of GNB. This kind of bionanocomposites might be used as novel bactericidal materials and we also provide an effective synthesis method for preparing functional bioconjugated nanoparticles here.     

STEREOSELCETIVE SYNTHESIS OF SOME NUCLEOSIDES

A new method for the synthesis of perbenzylated, peracetylated and perbenzoylated sugar nucleosides has been carefully studied. In this method trichloroacetoxy and trifluoroacetoxy groups were displaced efficiently in the reaction of nucleoside formation as leaving group. And this method was found to be widely applicable in the study of carbohydrate chemistry.     

Graphene-gold Nanoparticle Composite Film Modified Electrode for Determination of Trace Mercury in Environmental Water

The graphene-gold nanoparticles composite film modified glassy carbon electrode （EG- AuNPs/GCE） was prepared by one-step coelectrodeposition and employed for determination of trace mercury in environmental water with differential pulse stripping voltammetry. Such a nanostructured composite film combined with the advantages of gold nanoparticles and graphene, can greatly promote the electron-transfer process and increase accumulation abil-ity for Hg（Ⅱ）, leading to a remarkably improved sensitivity. The linear calibration curve ranged from 0.2 μg/L to 30 μg/L for Hg（Ⅱ） and the detection limit （S/N=3） was found to be 0.03 μg/L at a deposition time of 300 s. Moreover, the stablity of the as-prepared electrode and interferences from other substances were evaluated. The modified electrode was successfully applied to the direct detection of Hg（Ⅱ） in real water samples.     

Carbon-Supported Silver Catalysts for CO Selective Oxidation in Excess Hydrogen

Carbon materials were used as supports for Ag catalysts that are prepared using the conventional wet impregnation method, and their catalytic properties for CO selective oxidation in excess hydrogen at temperatures below 483 K were tested. A variety of techniques, e.g. N2 adsorption, XPS, TPD, UV-Vis DRS, TEM and SEM, were used to determine the influence of physical and chemical properties of the carbon on the properties of Ag catalyst. It was found that defects on the carbon surface served as nucleation sites for silver ions, while functional groups on carbon surface induced their reduction to the metallic form. The formation of silver particles on carbon was governed by homogeneous and/or heterogeneous nucleation during the impregnation and subsequent activation processes. The best catalytic performance was obtained with a Ag/carbon black catalyst with a uniform size distribution of silver nanoparticles (about 12 nm), moderate BET surface area (with a mesoporous structure), and a limited amount of carbon-oxygen groups. The research indicates that carbon materials are potentially good supports for silver catalysts for preferential oxidation of CO in excess hydrogen.     

The study of preconcentration and separation of vanadium(V) using microcrystalline triphenylmethane loaded with crystal violet and the determination of vanadium(V) in water samples by spectrophotometry

The paper describes a novel method for vanadium(V) preconcentration using microcrystalline triphenylmethane loaded with crystal violet (CV) prior to the determination by spectrophotometry. The effects of different parameters, such as the amounts of crystal violet and triphenylmethane, acidity, stirring time, various salts and metal ions etc on the enrichment yield of V(V) have been investigated to select the experimental conditions. V(V) can be completely separated from Cd(II), Pb(II), Mn(II), Co(II), Cu(II), Fe(III), Ni(II), Al(III), Zn(II) and Hg(II) by controlling acidity. Under the optimum conditions, V(V) can be totally adsorbed on the surface of microcrystalline triphenylmethane. The possible reaction mechanism of the enrichment of V(V) is discussed in detail in this paper. The detection limit of this proposed method is 0.023 μg L⁻¹ with the preconcentration factor of 200. The recovery is in a range of 96.0–104%. The proposed method has been successfully applied to the determination of trace vanadium in various water samples with satisfactory results.     

Mercuric ions induced aggregation of gold nanoparticles as investigated by localized surface plasmon resonance light scattering and dynamic light scattering techniques

With the development of nanosciences, both localized surface plasmon resonance light scattering (LSPR-LS) and dynamic light scattering (DLS) techniques have been widely used for quantitative purposes with high sensitivity. In this contribution, we make a comparison of the two light scattering techniques by employing gold nanoparticles (AuNPs) aggregation induced by mercuric ions. It was found that citrate-stabilized AuNPs got aggregated in aqueous medium in the presence of mercuric ions through a chelation process, resulting in greatly enhanced LSPR-LS signals and increased hydrodynamic diameter. The enhanced LSPR-LS intensity ( I) is proportional to the concentration of mercuric ions in the range of 0.4-2.5 M following the linear regression equation of I = 84.7+516.4c, with the correlation coefficient of 0.983 (n = 6) and the limit of determination (3 ) about 0.10 M. On the other hand, the increased hydrodynamic diameter can be identified by the DLS signals only with a concentration of Hg 2+ in the range of 1.0-2.5 M, and a linear relationship between the average hydrodynamic diameters of the resulted aggregates and the concentration of Hg 2+ can be expressed as d = 6.16 + 45.9c with the correlation coefficient of 0.994. In such case, LSPR-LS signals were further applied to the selective determination of mercuric ions in lake water samples with high sensitivity and simple operation.     

Study on Fmoc Solid-phase Synthesis and Activity of Thymosin α1

Thymosin α1 (Tα1), an immunologically polypeptide, [1] is highly acidic composed of 28 amino acid residues with acetylserine as the NH2 terminus. The MW of this peptide is 3108, with pI 4.2. There are many Asp and Glu in this molecule and the complete amino acid sequence of Tα1 is Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-IleThr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH. This peptide has potent biological activity and has been found to be 10～ 1000 times as active as thymosin F5. In this paper, a Tα1 has been synthe sized by a solid-phase method. Peptide synthesis was performed manually by the stepwise solid-phase method using the base-labile Fmoc group for protecting the α-amino acid. [2]     

Novel method for determining stacking disorder degree in hexagonal graphite by X-ray diffraction

The broadening effect of stacking disorder in hexagonal graphite is found experimentally by XRD to be identical to that of stacking faults in hexagonal-closed-packing(HCP) structure,which has obvious selective broadening effect.The Langford’s method for dealing with the twofold broadening effects of the crystallite-faults in hexagonal ZnO has been extended in this paper,and then applied to the deter-mination of stacking disorder in 2H-graphite,which indicates that our extension method is convenient to both ...     

Novel,efficient,and green procedure for the synthesis of 1,5-benzodiazepines catalyzed by MgBr_2 in aqueous media

MgBr_2 performs as a novel catalyst for the synthesis of various 1,5-benzodiazepine derivatives from wide range of substituted ophenylenediamines and various ketones in good to excellent isolated yields(93-98%)using water as solvent at ambient temperature.Several solvents were examined for this reaction;however,in terms of reaction yield and time,water was found to be the optimum solvent.The remarkable advantages offered by this method are easily and inexpensive available catalyst,simple procedure,mild c...     

One-pot synthesis of silver colloid with body-heat for surface-enhanced Raman spectroscopy detections

In this study, a convenient method of preparing the substrate is proposed with one-pot synthesis of silver colloid under body heat, and the SERS detection uses the fresh substrate to avoid the drawback of substrates' short life of use. The synthesis of silver colloid is carried out in a 10 mL vial by using ascorbic acid as a reductant and trisodium citrate as a stabilizer. The vial is grasped with the palm of the experimenter for several minutes without shaking. The proposed method is simple, rapid, green energy and cost-effective. By adjusting the concentration of trisodium citrate, not only the particle size can be controlled from about 110 nm to 50 nm but also the homogeneity of nanoparticles can be improved. As a SERS substrate, the silver colloid has high batch reproducibility and showed good SERS activity. The relative standard deviation between different manufacturers is 5.51% when the substrate of silver colloid is used for the detection of rhodamine 6 G. Using the substrate, the lowest detection concentrations of rhodamine 6 G, crystal violet, enrofloxacin, melamine and leucomalachite green are 1.0×10~(-8), 6.1×10~(-8),1.4 × 10~(-6), 7.1 ×10~(-5) and 5.1 ×10~(-8) mol/L, respectively. Results demonstrate that the developed method has the advantage of convenience and high efficiency in the field preparation of reliable SERS substrate.     

Fabrication of ZnO with tunable morphology through a facile treatment of Zn-based coordination polymers

The morphology and structure of zinc oxide(ZnO), one of the important semiconductors, are relevant to its properties and applications. The preparation of ZnO with tunable morphology and desired structure is an attractive topic in the field of material synthesis. This work reports a facile method for the synthesis of Zn O with controllable morphology and crystal orientation using Zn-based coordination polymer particles(Zn-CPP) as precursors. Using hydrothermal method, Zn-CPP with morphologies of microrod, nanoplate, flower-like, arrow-tipped microsheet, and square cylinder were successfully synthesized via the coordination between metal ions Zn2+ and organic ligand 1,4,5,8-naphthalenetetracarboxylic dianhydride in aqueous solution. Subsequent thermal treatment of the Zn-CPP successfully resulted in the formation of porous Zn O with similar morphology to Zn-CPP. It is also found that the Zn O with enhanced(002) orientation could be obtained from Zn-CPP with preferred(002) orientation. This strategy could be extended for the preparation of other metal oxides with desired shape and structure.     

Potentiometric determination of ultratrace amounts of fluoride enriched by zirconia in a flow system

A satisfactory method was described for separation and preconcentration of ultratrace amounts of fluoride ions enriched by zirconia (ZrO₂) as an inorganic ion exchanger. Fluoride ions can be adsorbed rapidly and selectively on zirconia from an acidic solution (pH 4.8) then reversibly desorbed by increasing pH up to 13. A flow system consisting of a column packed with zirconia impregnated on cellulose fibers and an ion-selective electrode was used for the determination of fluoride. The RSD was found to be 1.6% and the detection limit defined by S/N = 3 was 3 × 10⁻⁹ mol L⁻¹. The interference effects of various ions, such as nitrate, sulfate, halides, alkaline, and alkaline earth ions, which may be found in the environmental water, were studied, and it was found that they were tolerated even at high concentrations. The method was applied to determine fluoride in drinking water, which contains ultratrace amounts of fluoride. The concentration of fluoride was found to be 42 μg L⁻¹, which is confirmed by spiking 2 μmol fluoride to the drinking water with a recovery of 99%. Published in Russian in Zhurnal Analiticheskoi Khimii, 2006, Vol. 61, No. 2, pp. 179–183. The text was submitted by the authors in English.     

分光光度法同时测定两个干扰组份的研究 I.多波长数据线性回归法及其应用于同时测定微量锰和锌的探讨

In this paper, a linear regression method of multiwavelength data is proposed. The method, based on the difference of molar absorptivity between two coloured chelates at murti-wavelengths, can be applied to simultaneous spectrophotometric determination of two-interfering-component systems in the visible region. As an example, the availability as well as the optimum condition for simultaneous determination of Mn and Zn with 5-Br-PADAP in the presence of nonionic surfactant Triton X-100 have been studied. Measure the absorbance at 15 wavelengths over the range of 540-584 nm and treat the data with the suggested method, the linear correlation coefficients (γ) are found to be 0.998 in the synthetic mixtures containing microamounts of Mn and Zn with the concentration ratio from 1:10 to 10:1. The recoveries of both elements are 95-120% with the relative standard deviations (N=5) less than 17%. the method has been successfully used for direct determination of Mn and Zn in tap water. The new method proposed in this work is simple, fast and can be used for the analysis of two-interfering-component systems.     

InCl_3·4H_2O Catalyzed Aldol Condensation of Cycloalkanones with Aromatic Aldehydes

a, a-Bis (substituted) benzylidenecycloalkanones are widely used as precursors for synthesis of bioactive pyrimidine derivatives and their synthesis have attracted considerable attention1. Aldol condensation of cyclopentanone or cyclohexanone with aldehydes is employed, and the reactions were carried out in the presence of strong acids or bases2. Recently, the application of metal ions as catalyst in this type of reaction has been reported3. For example, RuCl3 has been reported to be an exc…     

Iron(III) Trifluoroacetate: Chemoselective and Recyclable Lewis Acid Catalyst for Diacetylation of Aldehydes,Thioacetalization and Transthioacetalization of Carbonyl Compounds and Aerobic Coupling of Thiols

Iron(III) trifluoroacetate [Fe(CF3CO2)3] was found to be a recyclable, highly efficient and chemoselective Lewis acid catalyst for protection of a variety of carbonyl compounds as thioacetals under nearly neutral conditions. With the use of this catalyst, 1,3-dithiolanes and 1,3-dithianes were obtained in high yields from various aldehydes. Under the same conditions ketones were similarly but more slowly thioketalized. This difference in reactivity between aldehydes and ketones was successfully utilized for the selective thioacetalization of aldehydes in the presence of ketones and also for the chemoselective conversion of β-diketone into the corresponding dithioacetal. Transthioacetalization of O,O-acetals and O,O-ketals into cyclic thioacetals was also achieved by using this catalyst. Additionally, iron(III) trifluoroacetate has been found to be efficient catalyst for the addition of acetic anhydride to both aromatic and aliphatic aldehydes to afford 1,1-diacetates (gem diacetates). Aerobic dimerization of thiols was achieved by this reagent mediated by sodium iodide and air atmosphere.