Trace Element Analysisin Compound

Trace　Element　Analysisin　Compound　...     

Schwefel in Erdöl: Ein problematisches Element?

In November 2002, the tanker Prestige sank west of Spain laden with about 77 000 tons of a heavy oil distillation residue that polluted beaches in Spain and France. The public was warned of its toxic properties, (falsely) said to be due to the sulfur. Sulfur is present in commercial crude oils to the extent of 0.1 – 4 %. It is derived from sulfate ions of sea water. Following reduction, it reacts with matter in sediments, ultimately leading to organic sulfur compounds. The removal of this sulfur is an important industrial process.     

Attractive π-Interaction as an Efficient Control Element for Acyclic Stereocontrol

During the course of our synthetic studies of a natural product, an indium-mediated allylation reaction in aqueous media has been developed as the key step for the assembly of the advanced intermediate 2 (Scheme 1) in our strategy. The reaction proceeds with very high diastereoselectivity (>99% de), a result rare for acyclic molecules in the absence of obvious steric interaction or intramolecular chelation.¹ The interlocking physical, chemical and computational studies undertaken supported a π-stacking effect between the phenyl ring with the ketone.     

A Multi‐Element Flow Injection System for Heavy Metals Determination

Abstract

A multi‐element flow injection (FI) system with spectrophotometric detection was developed for sequential determination of Zn(II), Cu(II), Cd(II), Pb(II), and Hg(II). Dithizone reagent was used for the previously mentioned analytes and it was prepared on line by using a solid reagent column (SRC). Bear in mind that the most hazardous elements for environmental contamination are lead, cadmium, and mercury; a multi‐element FI system with preconcentration steps is proposed to determine their trace levels in natural waters. Results obtained for different samples agreed satisfactorily with those obtained by the reference method inductively coupled plasma‐atomic emission spectrometry (ICP‐AES). Detection limits were 5.4, 5.0 and 14 µg L^?1 for Cd(II), Pb(II), and Hg(II), respectively. The percent of relative standard deviation (RSD) was better than 4.5% for each one.     

Element geochemistry of Holocene sediment and paleoenvironmental change in the Changjiang Estuary

Analyses of 41 elements reveal that Holocene sediments In the Changjiang Estuary bear regular elemental compositions in different sedimentary environments, and Holocene sediments came mainly from the Changjiang River based on compositions of REEs and most trace elements. Some heavy metals are more enriched in the surface sediment than in the deltaic sediments, reflecting human impact. Elemental compositions of the river channel sediment are related to the influence of proximal sediments. Sedimentary environments exert some influences on elemental compositions. Some chemical indices can be used to record chemical weathering undergone by the Changjiang sediment and environmental change.     

Yttrium and Rare Earth Element Complexation by Chloride Ions at 25°C

Formation constants for yttrium and rare earth element (YREE) chloride complexation have been measured at 25°C by examining the influence of medium (NaClO₄ and NaCl) on YREE complexation by fluoride ions and methyliminodiacetate (MIDA). YREE chloride complexation constants _Clβ₁(M) obtained in this work using dissimilar procedures are in good agreement and indicate that, at constant temperature and ionic strength, _Clβ₁(M) does not vary significantly across the fifteen-member series of elements. The ionic strength μ dependence of YREE chloride formation constants between 0 and 6 molar ionic strength can be written, for all YREE, as ${\text{log}}_{{\text{CI}}} \beta _1 \left( M \right) = \log _{{\text{CI}}} \beta _1^0 \left( M \right) - 3.066\mu ^{0.5} /\left( {1 + 1.727\mu ^{0.5} } \right)$ where _Clβ₁(M) = [MCl²⁺][M³⁺]^?1[Cl^?1]^?1 and log_Clβ₁ ^o(M) represents the MCl²⁺ formation constant for all YREE at zero ionic strength: log_Clβ₁ ^o = 0.65 ± 0.05.     

Oxyluciferin Photoacidity: The Missing Element for Solving the Keto–Enol Mystery?

The oxyluciferin family of fluorophores has been receiving much attention from the research community and several systematic studies have been performed in order to gain more insight regarding their photophysical properties and photoprotolytic cycles. In this minireview, we summarize the knowledge obtained so far and define several possible lines for future research. More importantly, we analyze the impact of the discoveries on the firefly bioluminescence phenomenon made so far and explain how they re‐open again the discussion regarding the identity (keto or enol species) of the bioluminophore.     

New Aspects in the Chemistry of Three-membered Ring Compounds Containing a Highly Coordinate Main Group Element

The title compounds were synthesized by taking advantage of the Martin ligand. Their structures were determined by X-ray crystallography. Pentacoordinate thiasiliranides were hydrolyzed to give the corresponding thiol. Pentacoordinate chalcogenaphosphiranes were found to have polar P-chalcogen bonds, which were confirmed by their reactions with CF3SO3Me to give the corresponding 1-（methylchalcogena）alkylphosphonium triflates and by the solvent-dependent NMR studies.     

Comprehensive Investigation of Yttrium and Rare Earth Element Complexation by Carbonate Ions Using ICP–Mass Spectrometry

Carbonate stability constants for yttrium and all rare earth elements have been determined at 25°C and 0.70 molal ionic strength by solvent exchange and inductively coupled plasma–mass spectrometry (ICP–MS). Measured stability constants for the formation of and from M³⁺ are in good agreement with previous direct measurements, which involved the use of radio-chemical techniques and trivalent ions of Y, Ce, Eu, Gd, Tb, and Yb. Direct ICP–MS measurements of and formation constants are also in general agreement with modeled stability constants for the metals La, Pr, Nd, Sm, Dy, Ho, Er, Tm, and Lu, based on linear-free energy relationship (LFER). The experimental procedures developed in this work can be used for assessing the complexation behavior of other geochemically important ligands such as phosphate, sulfate, and fluoride.     

Recent Developments in the Organic Chemistry of Calcium – An Element with Unlimited Possibilities in Organometallic Chemistry?

The organocalcium chemistry developed vastly during the last decade. The preparation of the organocalcium compounds via direct synthesis (insertion of Ca into a C‐X bond of phenyl halides, Grignard reaction) affords skilful procedures due to the inertia of the calcium metal and the extreme reactivity of the organocalcium derivatives. Further suitable preparative methods include metathesis reactions of CaX₂ with KR or LiR, metallation reactions of H‐acidic substrates, metal‐halogen exchange reactions, and transmetallation of heavy main group atoms in their compounds with calcium metal. Possibilities to stabilize organocalcium compounds include steric shielding by bulky ligands at the periphery and electronic reduction of the nucleophilicity of the calcium‐bound carbanions. Selected applications in catalysis such as hydrophosphination are also mentioned. Very recent developments and challenges in the preparation of alkaline earth metal(I) compounds are presented as well. Concepts to overcome the rather large atomization energies of the metals are discussed.     

Effects of Alkali Element Doping and Synthesis Conditions on the Genesis of the Phase Composition of Alumina–Chromium Catalysts

Kinetics and Catalysis - The influence of modifying additives and synthesis conditions on the genesis of the phase composition of alumina–chromium catalysts was studied by differential...     

Theoretical Study on Electron Transfer Matrix Element in Oxidation of α—Amino Carbon—Centered Radical by O2

As a successive work of our previous paper,^1the electron transfer matrix element(Vrp)in the oxidation of the simplified model molecule of α-amino carbon-centered radical by O2 has been investigated with ab initio calculation at the level of UHF/6-31 G**.Based on the optimized geometries of the reactgant and the ion-pair complex obtained previously,the reaction heat and the iuner reorganization energy have been obtained by constructing the potential energy curves of reactant and product states considering the solvent effect with the conductor-like screening model(COSMO).The solvent reorganization energy has been estimated using Lippert-Mataga relationship.The calculated results show that the value of Vrp is several times larger than that of RT,which means that the model reaction is an adiabatic one.Theoretical investigation indicates that the solvent effect on the direct electron transfer (ET) process of oxidation of α-amino carbon-centered radical by oxygen is remarkable.     

Electroconductivity and Ion Transport in Protonic Solid Electrolytes BaCe0.85R0.15O3–δ, where R is a Rare-Earth Element

The total, ionic, and protonic conductivities of solid electrolytes BaCe_0.85R_0.15O_{3 –} (BC15R), where R = Sc, Y, La, and all lanthanides bar Pm, are studied at ₂ = 2.1 × 10⁴–10^–15 Pa, ₂ = 2.1 × 10³ Pa, and temperatures of 550–1000°. The samples are synthesized in air at 1450° for two hours. In oxidizing media, all the electrolytes are mixed ion–hole conductors. In reducing environment, BC15R doped with R³⁺ exhibit oxygen–proton conduction. Ionic and protonic conductivities are independent of ₂. Protonic conductivity disobeys the Arrhenius dependence: it decreases with increasing temperature. The total and ionic conductivities of BC15R are virtually independent of the nature of cations R³⁺ in the interval from Nd to Lu.     

A Quantitative Determination of Atmospheric Deposition Sources in the “Campo de Gibraltar” Region,Using Factor Analysis and Chemical Element Balance

Abstract

Factor analysis and chemical element balance were employed to identify and quantify the major atmospheric deposition sources at 12 sampling stations in the “Campo de Gibraltar” Region. The data were best represented with 5 sources: soil, marine aerosol, residual fuel oil, refuse and limestone. Predicted concentrations account for about 80% of measured total deposition.     

Eine Zusammenstellung der chemischen Methoden zur Bestimmung des Oxydations- oder Reduktionsverm?gens von Stoffen, die ein Element in mehreren Oxydationsstufen enthalten

Ohne Zusammenfassung     

Balancing Donor-Acceptor and Dispersion Effects in Heavy Main Group Element π Interactions: Effect of Substituents on the Pnictogen⋅⋅⋅π Arene Interaction

High-level ab initio calculations using the DLPNO-CCSD(T) method in conjunction with the local energy decomposition (LED) were performed to investigate the nature of the intermolecular interaction in bismuth trichloride adducts with π arene systems. Special emphasis was put on the effect of substituents in the aromatic ring. For this purpose, benzene derivatives with one or three substituents (R=NO₂, CF₃, OCHO, OH, and NH₂) were chosen and their influence on donor-acceptor interaction as well as on the overall interaction strength was examined. Local energy decomposition was performed to gain deeper insight into the composition of the interaction. Additionally, the study was extended to the intermolecular adducts of arsenic and antimony trichloride with benzene derivatives having one substituent (R=NO₂ and NH₂) in order to rationalize trends in the periodic table. The analysis of natural charges and frontier molecular orbitals shows that donor-acceptor interactions are of π→σ* type and that their strength correlates with charge transfer and orbital energy differences. An analysis of different bonding motifs (Bi⋅⋅⋅π arene, Bi⋅⋅⋅R, and Cl⋅⋅⋅π arene) shows that if dispersion and donor-acceptor interaction coincide as the donor highest occupied molecular orbital (HOMO) of the arene is delocalized over the π system, the M⋅⋅⋅π arene motif is preferred. If the donor HOMO is localized on the substituent, R⋅⋅⋅π arene bonding motifs are preferred. The Cl⋅⋅⋅π arene bonding motif is the least favorable with the lowest overall interaction energy.