Determination of Lead, Chromium, Manganese and Zinc in Slurries of Botanical and Biological Samples by Electrothermal Atomic Absorption Spectrometry Using Tungsten-Containing Chemical Modifiers

Lead, Cr, Mn and Zn in slurries of botanic and biological samples were determined by electrothermal atomic absorption spectrometry (ETAAS) using W, Ir, NH₄H₂PO₄, W and NH₄H₂PO₄, Ir and NH₄H₂PO₄, W and Ir, and W + Ir + NH₄H₂PO₄ chemical modifiers in an 0.2% (v/v) Triton X-100 plus 0.2% (v/v) nitric acid mixture. Zeeman effect background correction was performed and platforms inserted into graphite tubes were used. Comprehensive comparative studies were carried out with respect to pyrolysis and atomization temperatures, atomization and background absorption profiles, characteristic masses, detection limits and accuracy of the determinations in the presence and absence of modifiers. The mixture of W + Ir + NH₄H₂PO₄ was found to be preferable for the determination of Pb, Cr, Mn and Zn in slurry samples. The pyrolysis temperatures of the analytes were increased up to 1250 °C for Pb, 1000 °C for Zn, 1400 °C for Cr and Mn by using W + Ir + NH₄H₂PO₄ with an 0.2% (v/v) Triton X-100 plus 0.2% (v/v) nitric acid mixture used as diluent solution. The optimum masses of the mixed modifier components were found to be 20 µg W + 4 µg Ir + 50 µg NH₄H₂PO₄. The characteristic masses of Pb, Cr, Mn and Zn obtained are 16.3, 5.6, 0.1 and 1.1 pg, respectively. The detection limits of Pb, Cr, Mn and Zn based on integrated absorbance for 0.5% (m v⁻¹) slurries were found to be 0.14, 0.06, 0.02 and 0.01 µg g⁻¹, respectively. The slurries of botanic and biological certified and standard reference materials were analyzed with and without the modifiers. Depending on the sample type, the percent recoveries increased from 63 up to 104% for analytes when using the proposed modifier mixture.     

Metal-binding properties of the peptide APP170-188: a model of the ZnII-binding site of amyloid precursor protein (APP)

Amyloid precursor protein (APP) plays a key role in Alzheimer's disease (AD), although the function of this membrane protein is still unclear. Metal ions are implicated in AD and they also interact with APP. APP possesses a strong ZnII binding site, which is evolutionary conserved. In this paper a synthetic peptide, APP170-188, with a sequence corresponding to the conserved ZnII-binding domain of APP, was synthesised and its metal-binding properties analysed. Titration experiments pointed to the binding of a stoichiometric amount of divalent ions. Further studies indicated that the binding of divalent metals like ZnII, CdII and CoII induces the dimerisation of the peptide. This dimer contains a dinuclear cluster in which the two divalent metals are bridged by two thiolate ligands from cysteine residues. The other two ligands of the tetrahedral coordination sites of each metal ion are terminal thiolate ligands. This structure was supported by the following arguments. The complex formed with CoII presents the characteristic features for tetrahedral tetrathiolate coordination in its UV-visible spectrum. The sequence of APP170-188 contains only three cysteine residues, which is incompatible with a monomeric CoII-APP170-188 complex. EPR measurements of the complex with one equivalent of CoII show almost no signal at 4 K, which is compatible with an antiferromagnetic spin-coupling of the metal ions in a cluster structure. Size-exclusion chromatography indicated that the elution time for the complexes with ZnII and CdII corresponds to the expected molecular weight of a dimer. The circular dichroism (CD) spectrum of the complex with one equivalent of CdII shows a band at 265 nm+, and an ellipticity similar to those observed for similar CdII-thiolate clusters. Possible biological implications of the ZnII binding site and the metal-induced dimerisation are discussed.     

A ratiometric fluorescent probe for zinc ions based on the quinoline fluorophore

A ratiometric fluorescent zinc probe 1 of carboxamidoquinoline with a carboxylic acid group was designed and synthesised. Probe 1 exhibits high selectivity for sensing Zn²⁺; about a 13-fold increase in fluorescence emission intensity and an 82?nm red-shift of fluorescence emission are observed upon binding Zn²⁺ in EtOH/H₂O (1?:?1, V/V) solution. The ratiometric fluorescence response is attributed to the 1?:?1 complex formation between probe 1 and Zn²⁺ which has been utilised as the basis for the selective detection of Zn²⁺. The analytical performance characteristics of the proposed Zn²⁺-sensitive probe were investigated. The linear response range covers a concentration range of Zn²⁺ from 2.0?×?10^?6 to 5.0?×?10^?5?mol?L^?1 and the detection limit is 2.7?×?10^?7?mol?L^?1. The determination of Zn²⁺ in both tap and river water samples shows satisfactory results.     

Determination of zinc in marine/lacustrine sediments by graphite furnace atomic absorption spectrometry using Pd/Mg chemical modifier and slurry sampling

Effectiveness of Pd/Mg chemical modifier for the accurate direct determination of zinc in marine/lacustrine sediments by graphite furnace atomic absorption spectrometry (GF-AAS) using slurry samples was evaluated. A calibration curve prepared by aqueous zinc standard solution with addition of Pd/Mg chemical modifier is used to determine the zinc concentration in the sediment. The accuracy of the proposed method was confirmed using Certified Reference Materials, NMIJ CRM 7303-a (lacustrine sediment) from National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Japan, and MESS-3 (marine sediment) and PACS-2 (marine sediment) from National Research Council, Canada. The analytical results obtained by employing Pd/Mg modifier are in good agreement with the certified values of all the reference sediment materials. Although for NRC MESS-3 an accurate determination of zinc is achieved even without the chemical modifier, the use of Pd/Mg chemical modifier is recommended as it leads to establishment of a reliable and accurate direct analytical method. One quantitative analysis takes less than 15 minutes after we obtain dried sediment samples, which is several tens of times faster than conventional analytical methods using acid digested sample solutions. The detection limits are 0.13?µg?g^?1 (213.9?nm) and 16?µg?g^?1 (307.6?nm), respectively, in sediment samples, when 40?mg of dried powdered samples are suspended in 20?mL of 0.1?mol?L^?1 nitric acid and a 10?µl portion of the slurry sample is measured. The precision of the proposed method is 8–15% (RSD).     

Synthesis of Poly (methyl methacrylate)/Zinc Oxide Nanocomposite with Core-Shell Morphology by Atom Transfer Radical Polymerization

A method to prepare zinc oxide (ZnO) nanoparticles with a covalently bonded poly(methyl methacrylate) (PMMA) shell by surface initiated atom transfer radical polymerization (ATRP) was reported. First, the initiator for ATRP was covalently bonded onto the surface of zinc oxide nanoparticles through our novel method. Firstly, the surface of ZnO nanoparticle was treated with 3-aminopropyl triethoxysilane, a silane coupling agent, and then this functionalization nanoparticle was reacted with α-chloro phenyl acetyl chloride to prepare atom transfer radical polymerization macroinitiator. The metal-catalyzed radical polymerization of MMA with ZnOmacroinitiator was performed using a copper catalyst system to give the ZnO-based nanoparticles hybrids linking PMMA segments (poly (methyl methacrylate)/zinc oxide nanocomposite). These hybrid nanoparticles had an exceptionally good dispersability in organic solvents and were subjected to detailed characterization using FTIR, TEM and TGA and DSC analyzed.     

基于四氟对苯二甲酸为配体的两个锌(Ⅱ)的配合物的合成、晶体结构和荧光性质

本文以四氟对苯二甲酸(H2tfbdc)和2,2′-联吡啶(bpy)为配体,合成了2个锌(Ⅱ)的配合物[Zn2(bpy)4(Htfbdc)2(tfbdc)](1)and[Zn(bpy)(H2O)2(tfbdc)](2)。并用元素分析、红外光谱、X-射线单晶衍射结构分析、热重分析等对其进行了表征。化合物1和2均属于三斜晶系,空间群为P1。配合物1和2中的锌(Ⅱ)离子分别位于畸变的八面体和畸变的三角双锥构型中。配合物1为双核结构,它们通过分子间氢键进一步形成一个二维的结构;配合物2是一个单核的两性离子,两性离子间通过氢键形成一个三维的空间网状超分子结构。考察了两种配合物的固体荧光性质。     

三维锌配位聚合物的合成、晶体结构及与DNA的作用

在水热条件下,由联苯-2,4,4',6-四甲酸(H₄bptc),4,4'-联吡啶(bipy),合成了3种锌配位聚合物[Zn(bptc)_0.5]_n (1),[Zn₂(bptc)(H₂O)₃]_n·nH₂O (2),[Zn₂(bptc)(H₂O)(bipy)_1.5]_n·nH₂O (3),用元素分析、红外光谱等方法对配合物的组成进行了表征,并通过单晶X-射线衍射方法测定了配合物的晶体结构.结果表明:配合物1具有双核结构,八元环金属簇Zn₂(COO)₂²⁺自组装成具有(6,6)-连接拓扑结构;配合物2具有(4,5,6)-连接拓扑结构;配合物3在辅助配体的构筑下形成三维网络结构.用溴化乙锭荧光探针法测试了配合物对EB-DNA复合体系的荧光猝灭效应,实验结果显示配合物均能使EB-DNA复合体系的荧光发生不同程度的猝灭,由此推测配合物均与DNA发生了不同程度的插入作用,引入具有刚性平面辅助配体之后的配合物3,其作用力又强于不加辅助配体的配合物1和2.     

镍锌铁氧体/膨胀石墨/聚苯胺复合物的电磁损耗性能

用化学共沉淀法和原位乳液聚合法分别制备了镍锌铁氧体(Ni_xZn_1-xFe₂O₄)、Ni_0.7Zn_0.3Fe₂O₄/膨胀石墨(NZF/EG)二元复合物及其聚苯胺(PANI)包覆的三元复合物(NZF/EG/PANI)。用现代测试技术表征了样品的组成、结构、形貌和电磁性能。结果表明,NZF粒子较好地嵌入到EG的层间,PANI对NZF/EG的包覆效果良好;三元复合物的磁性能随磁性组分含量的减小而减弱,而电导率与EG和PANI的导电性及其相对含量相关联;复合物的电磁损耗性能优良,其中三元复合物优于二元复合物。含PANI 70wt%的NZF/EG/PANI三元复合物,制样厚度分别为1.5、2.0和2.5 mm时,其反射损耗峰值(有效带宽)分别为-19.99 dB(5.82 GHz),-20.33 dB (4.08 GHz)和-25.28 dB(3.67 GHz),具有优良的电磁波吸收效果。