Beer Digestions for Metal Determination by Atomic Spectrometry and Residual Organic Matter

Many standard and official sample digestion procedures for trace metal determination are carried out in open vessels on hot plates. A new procedure for the determination of trace metals by flame atomic absorption spectrometry or inductively coupled plasmaatomic emission spectrometry in beer samples was developed to be performed in closed reactors assisted by microwaves. The results are compared with the ones obtained by other procedures by means of the analysis of the variance. The differences between the procedures are attributed to residual organic matter. Voltammetry, absorption molecular spectrophotometry and high pressure liquid chromatography with a photodiode array detector are used to study the nature of these residues. Nitrobenzoic acids, phenolic acids and other organic compounds are often present after digestion. The results obtained are related to the precision in metal determination by atomic spectrometry. The need for elaboration of certified reference materials for trace metals in beer is suggested.     

Tetramethyldisilan-1,2-diyl-verbrückte Dicyclopentadienyl-und Diindenylmetalldichloride der 4. Gruppe – Kristallstruktur von

Tetramethyldisilane-1,2-diyl bridged Dicyclopentadienyl and Diindenyl Metal Dichlorides of the Group 4 Metals – Crystal Structure of Dicyclopentadienyl and diindenyl metal dichlorides of the type Cp′? SiMe₂SiMe₂? Cp′MCl₂ (Cp′ = C₅H₄, M = Ti ( 1 ), Zr ( 2 ), Hf ( 3 ); Cp′ = C₉H₇, M = Zr ( 4 ), Hf ( 5 )) were synthesized and characterized by means of their ¹H, ¹³C, ²⁹Si-n.m.r., MS, and IR spectra. The crystal structure of 2 was determined.     

Bis(crown-6)calix[4]arene/Cs+ Coordination Chemistry in NPME Solution

NMR spectroscopy was used to show that the symmetry of the crown ether bis(C6) is increased by an increase of the alkali metal cation radius. The EXAFS spectrum demonstrates that a seven oxygen atom coordinated configuration is present in the bis(C6)/Cs⁺/NPME system, where NPME denotes o-nitrophenylmethyl ether. The seventh oxygen in this complex, besides the six crown ether oxygens of bis(C6), may come either from a H₂O molecule or an NO₃⁻ ion.     

Synthesis and Mesogenic Properties of Liquid Crystals Containing Terminal Cyclohexylmethanol,Cyclopentylmethanol, Cyclobutylmethanol and Cyclopropylmethanol Moiety

Four series of compounds 11?50 containing terminal alicyclic rings such as cyclohexylmethyl, cyclopentylmethyl, cyclobutylmethyl, and cyclopropylmethyl rings were synthesized and their liquid crystal behavior studied. The ring size and the length of flexible alkoxy chain influence the phase formation in different ways. While the smaller ring and the shorter alkoxy chain tend to favor the formation of the N phase, the larger ring and the longer alkoxy chain tend to favor the formation of the SmC phase. All the compounds except 11 and 21 exhibit SmA phases. The widest temperature range of the N, SmA, and SmC phases are found in the compounds 41 , 46 , and 20 , respectively, which are 75 °C for 41 , 115 °C for 46 , and 100 °C for 20 .     

Clinical applications of chemiluminescence

This article reviews the clinical applications of chemiluminescence in routine testing and surveys the diverse applications of chemiluminescence in clinical research. In routine clinical testing, chemiluminescent labels (acridinium ester, acridinium sulfonamide) and detection reactions for peroxidase and alkaline phosphatase enzyme labels (luminol and adamantyl 1,2-dioxetane-based reactions, respectively) are widely used in immunoassay and nucleic acid probe assays (e.g. hybridization protection assay, Hybrid Capture^® assay). In clinical research the sensitivity, dynamic range and diversity of chemiluminescent assays has led to a vast range of applications, notably in protein and nucleic acid blotting, microarray-based assays, monitoring reactive oxygen species, and as detection reactions for substances separated by HPLC, capillary electrophoresis (CE), and flow-injection analysis.     

DSC Study of Polyurethanes obtained from 4,4'-Bis(10-Hydroxydecaoxy)biphenyl

The melting and crystallization of a series of polyurethanes derived from poly(1,6-hexylene adipate)diol (PHA), 4,4'-dicyclohexylomethane diisocyanate (HMDI) and 4,4'-bis(10-hydroxydecaoxy)biphenyl (BHDBP) as a chain extender were investigated by using DSC. Thermal properties of the polyurethanes were found to be strongly influenced by the hard segment content. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diastereoselective hydroformylation of 2-substituted allylic o-DPPB-esters-on the origin of 1,2-asymmetric induction

2-Substituted secondary alcohol o-DPPB esters (o-DPPB=ortho-diphenylphosphanylbenzoyl) have been prepared and their o-DPPB-directed diastereoselective hydroformylation examined. It was found that the diastereoselectivity increased as a function of the steric demand of the substituents both at the stereogenic center and in the alkene 2-position. Hydrolytic cleavage of the o-DPPB group afforded-via the lactols 29-the corresponding lactones 30, the relative configurations of the vicinal stereogenic centers of which were ascertainable by 2D-NOESY spectroscopy. In addition, a crystal structure analysis of the hydroformylation product 2 d provided further confirmation of the relative configuration. Replacement of the ester carbonyl group of the o-DPPB by a methylene unit resulted in significantly worse diastereoselectivity in the course of the hydroformylation (34-->35), which indicates a decisive role for the ester carbonyl function. All the experimental observations were combined in a model of the origin of the 1,2-asymmetric induction during the title reaction. The key feature is the consideration of diastereomeric trigonal-bipyramidal rhodium-hydrido-olefin complexes I and II, capable on the basis of the Hammond postulate of acting as good models for the transition states of the selectivity-determining hydrometalation step. Investigation of these complexes by force-field methods indicated good correlation between theoretically predicted and experimentally determined diastereoselectivities.     

聚4-重氮基苯乙烯与聚苯乙烯磺酸钠的自组装

1991年Ｄｅｃｈｅｒ等将带相反电荷的聚电解质 ,于水溶液中交替沉积在片基上 ,制备了多层超薄膜[1] ,这种制膜方法现称为静电自组装 .它操作简单 ,无需专用设备 ;一般在水体系进行 ,对环境友好 ;静电力比范德华力强 ,使它比ＬＢ膜稳定 ,所以近年来有很大发展[2 ] .现在自组装成膜驱动力已从静电力扩展到氢键力、电荷转移相互作用、疏水相互作用等 ,用于组装的组分也从聚电解质扩展到多官能团小分子、胶体粒子、无机纳米颗粒 ,ＤＮＡ、蛋白质等生物大分子等[3～ 11] .虽然自组装膜比ＬＢ膜稳定 ,但它也不耐极性溶剂、电解质水溶液等侵蚀 .如…     

四氢呋喃-水-乙醇三元溶液体系制备高合金化Pt-Ru/CMK-3催化剂

提出了在四氢呋喃(THF)、H2O和乙醇三元体系中用一般的化学还原法在室温下制备高合金化Pt-Ru/CMK-3催化剂的新方法. 与在纯水中制得的商品化ETEK催化剂相比, 其Pt-Ru粒子的合金化程度高、平均粒径较小且相对结晶度低, 因此, 该催化剂对甲醇氧化的电催化活性远高于在纯水中制得的Pt-Ru催化剂. 高合金化程度的原因是H2PtCl6和RuCl3在THF、H2O和乙醇三元溶液体系中的起始还原电位相近. 此外, CMK-3以其规整的二维有序孔道结构, 为直接甲醇燃烧电池(DMFC)中电子和物质的传输提供了方便的路径, 其巨大的比表面积也为Pt-Ru 纳米粒子的均匀分散提供了良好的载体.