Speciation of metal(loid)s in environmental samples by X-ray absorption spectroscopy: A critical review

Element specificity is one of the key factors underlying the widespread use and acceptance of X-ray absorption spectroscopy (XAS) as a research tool in the environmental and geo-sciences. Independent of physical state (solid, liquid, gas), XAS analyses of metal(loid)s in complex environmental matrices over the past two decades have provided important information about speciation at environmentally relevant interfaces (e.g. solid–liquid) as well as in different media: plant tissues, rhizosphere, soils, sediments, ores, mineral process tailings, etc. Limited sample preparation requirements, the concomitant ability to preserve original physical and chemical states, and independence from crystallinity add to the advantages of using XAS in environmental investigations. Interpretations of XAS data are founded on sound physical and statistical models that can be applied to spectra of reference materials and mixed phases, respectively. For spectra collected directly from environmental matrices, abstract factor analysis and linear combination fitting provide the means to ascertain chemical, bonding, and crystalline states, and to extract quantitative information about their distribution within the data set. Through advances in optics, detectors, and data processing, X-ray fluorescence microprobes capable of focusing X-rays to micro- and nano-meter size have become competitive research venues for resolving the complexity of environmental samples at their inherent scale. The application of μ-XANES imaging, a new combinatorial approach of X-ray fluorescence spectrometry and XANES spectroscopy at the micron scale, is one of the latest technological advances allowing for lateral resolution of chemical states over wide areas due to vastly improved data processing and detector technology.     

Highly stereoselective synthesis of (Z)-3-methoxy-1-methyleneisoindoles via DMAP catalyzed cyclization of methyl 2-alkynylbenzimidates

A DMAP (4-dimethylaminopyridine) catalyzed cyclization of methyl 2-alkynylbenzimidates has been developed, which affords 3-methoxy-1-methyleneisoindoles with excellent Z-stereoselectivity under mild and transition-metal-free conditions. The (Z)-3-methoxy-1-methyleneisoindole products can be converted to corresponding 3-amino-1-methyleneisoindoles, 3-methoxy-isoindoles, 3-methyleneisoindolinones and isoindolinones with high efficiency.     

Synthese,Charakterisierung und Struktur von Mn3SiO4F2

Synthesis, Characterization, and Structure of Mn₃SiO₄F₂ Mn₃SiO₄F₂ was synthesized by chemical vapour transport in a temperature gradient (800 → 700 °C) using MnF₂ as precursor and iodine as transport agent. SiO₂ was provided from the wall of the used silica tubes. The chemical composition of the crystals was determined by EELS and EDX analysis. The structure of Mn₃SiO₄F₂ was determined and refined to R(|F|) = 0.039, wR(F²) = 0.087, respectively. The orthorhombic phase crystallizes in the space group Pnma (No. 62) with a = 10.758(2) Å, b = 9.145(1) Å, c = 4.850(1) Å and Z = 4. Two crystallographically different Mn‐atoms are surrounded by oxygene and fluorine octahedrally. Si is tetrahedrally surrounded only by oxygen. IR‐measurements proved that in Mn₃SiO₄F₂ no substitution of F^– by OH^– takes place as in the mineral norbergite (Mg₃SiO₄(OH,F)₂).     

A one-step conversion of isoquinolinium salts into naphthalene derivatives1

Berberine chloride (1) upon treatment with NaOAc-Ac₂O yields naphthalene derivatives 4 and 5 In like fashion, 8 gives naphthalene 10; isoquinoline methiodide leads to β-naphthyl acetate; and 12 provides 14. The reaction has been extended to the 3-carbonyl pyridinium series where 3-acetylpyridine methiodide and 3-pyridinecarboxaldehyde methiodide furnish lactones 16 and 17, respectively. All these transformations proceed by initial nucleophilic attack of the acetic anhydride anion on the immonium carbon atom.     

The behavior of a many-particle electrode in a lithium-ion battery

We study a rechargeable lithium-ion battery that uses a many-particle FePO₄ electrode to reversibly store lithium atoms. This process is accompanied by a phase transition and charging/discharging run along different paths, so that hysteretic behavior is observed.Although there are experimental studies suggesting that the overall behavior of the battery is a many-particle effect, most authors exclusively describe the phase transition within a single particle model of the electrode.In this work, we study in detail a many-particle model for the electrode. The model is capable to describe a kind of phase transition where each individual particle of the electrode is homogeneous. It will be shown that the particles are either in the first phase or in the second phase. This phenomenon is due to the non-monotone relation between the chemical potential and the lithium mole fraction of a single particle.The pressure-radius relation of a spherical elastic rubber balloon also exhibits non-monotone behavior. In fact, a system of many interconnected balloons behaves correspondingly to an electrode consisting of many storage particles. The analogy between the two systems is important, because the predictions of the many-particle model can easily be tested with rubber balloons of macroscopic size than with an ensemble of microscopically small (FePO₄) particles.     

Experimental Investigation on the Mass Diffusion Behaviors of Calcium Oxide and Carbon in the Solid-State Synthesis of Calcium Carbide by Microwave Heating

Microwave (MW) heating was proven to efficiently solid-synthesize calcium carbide at 1750 °C, which was about 400 °C lower than electric heating. This study focused on the investigation of the diffusion behaviors of graphite and calcium oxide during the solid-state synthesis of calcium carbide by microwave heating and compared them with these heated by the conventional method. The phase compositions and morphologies of CaO and C pellets before and after heating were carefully characterized by inductively coupled plasma spectrograph (ICP), thermo gravimetric (TG) analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The experimental results showed that in both thermal fields, Ca and C inter-diffused at a lower temperature, but at a higher temperature, the formed calcium carbide crystals would have a negative effect on Ca diffusion to carbon. The significant enhancement of MW heating on carbon diffusion, thus on the more efficient synthesis of calcium carbide, manifested that MW heating would be a promising way for calcium carbide production, and that a sufficient enough carbon material, instead of CaO, was beneficial for calcium carbide formation in MW reactors.     

Growth of Single-walled Carbon Nanotubes on Substrates Using Carbon Monoxide as Carbon Source

The growth of single-walled carbon nanotubes(SWCNTs) on substrates has attracted great interests because of the potential applications in various fields. Carbon monoxide(CO) was used as the carbon source for the growth of SWCNTs on silicon substrates. Random or oriented SWCNTs can be produced by varying the CO flow rate. When the flow rate of CO was as low as 20 sccm(sccm:standard cubic centimeter per minute), dense SWCNT networks with clean surface were produced. When the flow rate was above 50 sccm, vertically aligned SWCNT(VA-SWCNT) arrays were grown. Well-aligned VA-SWCNT arrays were obtained in the temperature range of 650-800℃ and the content of large-diameter(above 1.7 nm) tubes in the array increased with the temperature. The height of the array was affected by the growth temperature, the CO flow rate, and the growth time. These findings indicate CO can be used as an efficient carbon source for the growth of SWCNTs on substrates under low flow rates.     

Contemporary Approaches to α,β-Dehydroamino Acid Chemical Modifications

As one of the most common unnatural amino acids(uAAs), α, β-dehydroamino acids(α,β-dhAAs) can be found in various ribosomally synthesized and post-translationally modified peptides(RiPPs) and other naturally occurring peptides. In recent years, novel reactions for α,β-dhAA modification continue to emerge. Due to their unique electrophilicity different from 20 natural amino acids, α,β-dhAAs, especially dehydroalanine(Dha), have become powerful tools for site-selective protein modification. In this review, we mainly focus on the latest research progress of C-C and C-heteroatom(C-X, X=S, N, Se, Si, P, B) bond formation methods based on α,β-dhAAs in the past five years. Particularly, we pay much attention to the α,β-dhAA derivatization methodologies used in the late-stage modification for natural peptides and proteins. In addition, we also focus on the downstream functionalization and therapeutic biologic applications of these modifications.     

Properties of polymer blends and triblock copolymers obtained by neutron scattering

Static and dynamic scattering properties of polymer blends and block copolymers are examined within the random phase approximation (RPA). A self-consistent theoretical scheme for a simultaneous analysis of elastic and quasielastic scattering data is presented. The case of a triblock copolymer made of an ordinary central block and two deuterated lateral blocks in a matrix of deuterated homopolymers is considered in detail. The theoretical predictions of the RPA are compared with the experimental data obtained by elastic neutron scattering experiments using mixtures of deuterated poly(dimethylsiloxane) homopolymers and copolymers made of three blocks of approximately equal sizes. The lateral blocks are deuterated poly(dimethylsiloxane) and the central one is an ordinary poly(dimethylsiloxane). A good agreement is found in the whole range of wavevectors covered by the experiments. An extension of the RPA to the analysis of the dynamical scattering data for the same systems is put forward. It is shown how the time relaxations of the bare response functions obtained from the single chain dynamics are used to extract the intermediate scattering function characterizing the system of interacting chains. © 1996 John Wiley & Sons, Inc.     

Application of Natural Clinoptilolite for Ammonium Removal from Sludge Water

Sludge water (SW) arising from the dewatering of anaerobic digested sludge causes high back loads of ammonium, leading to high stress (inhibition of the activity of microorganisms by an oversupply of nitrogen compounds (substrate inhibition)) for wastewater treatment plants (WWTP). On the other hand, ammonium is a valuable resource to substitute ammonia from the energy intensive Haber-Bosch process for fertilizer production. Within this work, it was investigated to what extent and under which conditions Carpathian clinoptilolite powder (CCP 20) can be used to remove ammonium from SW and to recover it. Two different SW, originating from municipal WWTPs were investigated (SW1: c₀ = 967 mg/L NH₄-N, municipal wastewater; SW2: c₀ = 718–927 mg/L NH₄-N, large industrial wastewater share). The highest loading was achieved at 307 K with 16.1 mg/g (SW1) and 15.3 mg/g (SW2) at 295 K. Kinetic studies with different specific dosages (0.05 g_CLI/mg_NH4-N), temperatures (283–307 K) and pre-loaded CCP 20 (0–11.4 mg/g) were conducted. At a higher temperature a higher load was achieved. Already after 30 min contact time, regardless of the sludge water, a high load up to 7.15 mg/g at 307 K was reached, achieving equilibrium after 120 min. Pre-loaded sorbent could be further loaded with ammonium when it was recontacted with the SW.