Identification of selenium species in urine by ion-pairing HPLC–ICP–MS using laboratory-synthesized standards

This study focused on the detection/identification of possible selenium metabolites in human urine. Organoselenium compounds not commercially unavailable were synthesized and characterized by electrospray mass spectrometry. Separation of selenomethionine, methylselenomethionine, trimethylselonium, selenoethionine, and selenoadenosylmethionine was achieved by ion-pairing HPLC with a mobile phase of 2 mmol L^–1 hexanesulfonic acid, 0.4% acetic acid, 0.2% triethanolamine (pH 2.5), and 5% methanol. The column effluent was introduced on-line to inductively coupled plasma–mass spectrometry for selenium-specific detection (⁷⁷Se and ⁷⁸Se). For selenium speciation in urine, solid-phase extraction was carried out using C₁₈ cartridges modified with hexanesulfonic acid. Selective retention of cationic species was observed from acidified urine (perchloric acid, pH 2.0). After elution with methanol, evaporation, and dissolution in the mobile phase, the sample was introduced to the HPLC–ICP–MS system and the chromatographic peaks were assigned by adding standards. The species identified in urine were selenomethionine, trimethylselonium ion, and selenoadenosylmethionine. The last species was detected for the first time and our results suggest that selenomethionine might enter the metabolic pathway of its sulfur analog in the activated methylation cycle.Kazimierz Wrobel and Katarzyna Wrobel are on the leave from the Institute of Scientific Research, University of Guanajuato, L. de Retana No. 5, 36000 Guanajuato, Gto., Mexico     

Polymeric bis(phosphonomethyl­carboxylato)calcium(II) at 85 K

In the crystal structure of the title compond, alternatively called poly[calcium(II)‐di‐μ‐carboxymethylphosphonato], [Ca(C₂H₄O₅P)₂]_n or [Ca(H₂AP)₂]_n, one of the phosphonate O atoms of the phosphonocarboxylate monoanion lies nearly antiperiplanar (ap) to the carboxylic acid C atom. The phosphonate P atom is located −sc and +ac relative to the carboxylic acid O atoms. The overall structure has a layered architecture. The Ca²⁺ cations lie on a twofold axis and are bridged by the phosphonate O atoms to form chains along the c axis, giving layers parallel to (100). There are medium‐strength O—H⃛O and C—H⃛O hydrogen‐bonding interactions stabilizing the layers, and O—H⃛O hydrogen bonds connect adjacent layers.     

Radionuclides and heavy metal concentrations as complementary tools for studying the impact of industrialization on the environment

The aim of the study was to determine whether using chemical and radiochemical analysis of lake sediments can highlight changes in the climate. Also it was studied whether human impact on the environment can be observed and to what extent such changes are in agreement with historical data. Samples of 16 cm thick sediment cores from the Smreczynski Staw Lake were collected and divided into 1 cm thick sub-samples. The samples were air dried and homogenized. The quantitative analysis of Fe, Mn, Zn, Cr, Cu, Ni, Cd, and Pb in the digested sediment samples was made by using atomic absorption spectrometry. Simultaneously, the radioactivity of ¹³⁷Cs using gamma spectrometry and ²¹⁰Pb_uns using alpha spectrometry, were measured for sediment layer dating. Results showed that iron concentration was in the range 0.3–over 1 % (w/w), and zinc 0.01–0.05 % (w/w). Lesser concentrations were found for copper 18.37–43.6 ppm, manganese 37.5–50.7 ppm, lead 146.1–432 ppm, chromium 12.3–37.4 ppm, nickel 3.1–10.8 ppm and cadmium 0.9–34.6 ppm. Changes in ¹³⁷Cs radioactivity was in the range of 89 ± 11 to 865 ± 62 (Bq kg^?1). Sediments composition can accurately reflect (in terms of time and to what extent) air pollution and natural geo-chemical processes in the environment. However, the choice of the analysed object is crucial in this respect. The Smreczynski Staw Lake, due to its location in the mountains and hydrological situation, proved to be very useful for providing undisturbed analytical samples.     

Mathematical models of solute retention in gas chromatography as sources of thermodynamic data. Part III. Alkylbenzenes as the test analytes

Direct determination of thermodynamic data has always been a complicated and troublesome experimental task. Gas chromatography is among long-established working tools well suited to performing this particular task indirectly. Our own results were first presented in the papers by Ciazynska-Halarewicz and Kowalska (1,2), and this article is Part III in the series. Present experiments are carried out on low- and medium-polarity stationary phases at five different temperatures ranging from 323K to 423K. They enable determination of two thermodynamic properties of the alkylbenzenes, molar enthalpy of vaporization (DeltaH(vap)), and the chemical potential of partitioning of the methylene group between the two phases of the chromatographic system (Delta micro (p(-CH2-))). These properties are obtained from eight nonempirical models and, as is apparent from their derivation (3-7), the terms of the models have clearly defined physical meaning, which enables calculation of thermodynamic properties.     

Evolution of Oxygen–Metal Electron Transfer and Metal Electronic States During Manganese Oxide Catalyzed Water Oxidation Revealed with In Situ Soft X‐Ray Spectroscopy

Manganese oxide (MnO_x) electrocatalysts are examined herein by in situ soft X‐ray absorption spectroscopy (XAS) and resonant inelastic X‐ray scattering (RIXS) during the oxidation of water buffered by borate (pH 9.2) at potentials from 0.75 to 2.25 V vs. the reversible hydrogen electrode. Correlation of L‐edge XAS data with previous mechanistic studies indicates Mn^IV is the highest oxidation state involved in the catalytic mechanism. MnO_x is transformed into birnessite at 1.45 V and does not undergo further structural phase changes. At potentials beyond this transformation, RIXS spectra show progressive enhancement of charge transfer transitions from oxygen to manganese. Theoretical analysis of these data indicates increased hybridization of the Mn?O orbitals and withdrawal of electron density from the O ligand shell. In situ XAS experiments at the O K‐edge provide complementary evidence for such a transition. This step is crucial for the formation of O₂ from water.     

Synthesis of Tri‐ and Difluoromethoxylated Compounds by Visible‐Light Photoredox Catalysis

Trifluoromethoxy (OCF₃) and difluoromethoxy (OCF₂H) groups are fluorinated structural motifs that exhibit unique physicochemical characteristics. Incorporation of these substituents into organic molecules is a highly desirable approach used in medicinal chemistry and drug discovery processes to alter the properties of a parent compound. Recently, tri‐ and difluoromethyl ethers have received increasing attention and several innovative strategies to access these valuable functional groups have been developed. The focus of this Minireview is the use of visible‐light photoredox catalysis in the synthesis of tri‐ and difluoromethyl ethers. Recent photocatalytic strategies for the formation of O?CF₃, C?OCF_3, O?CF₂H, and C?OCF₂H bonds as well as other transformations leading to the construction of OR_F groups are discussed herein.     

Differential pulse voltammetry in analysis of disinfectants — 2-mercaptobenzothiazole, 4-chloro-3-methylphenol, triclosan, chloramine-T

The aim of this work was to study the possibility of simultaneous voltammetric determination of some disinfectants used as components in cosmetic products. The examined compounds were: triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol), chloramine-T (N-chloro-p-toluenesulfonamide sodium salt), 4-chloro-3-methylphenol and 2-mercaptobenzothiazole. Measurements were performed using glassy carbon electrode immersed in Britton-Robinson buffers which acted as supporting electrolytes. The dependence of oxidation and reduction potentials on pH was examined using cyclic voltammetry. Britton-Robinson buffer of pH 9.9 was chosen for further studies to ensure the best separation of compounds. The resultant oxidation potentials indicate the possibility to simultaneously determine some of the disinfectants.. Oxidation reactions of mixtures containing two compounds (4-chloro-3-methylphenol and chloramine-T, 2-mercaptobenzothiazole and 4-chloro-3-methylphenol, 2-mercaptobenzothiazole and triclosan) were recorded as differential pulse voltammograms.     

Dynamic Light Scattering and NMR Studies of Napin

We analyze the structure of napin (BngNAP1), a storage protein (m.w. 14.5 kDa) from Brassica napus. On the basis of the results of ¹H NMR spectroscopy and dynamic light scattering (DLS) studies, the overall shape and secondary structure of the molecule are estimated.     

5,5‐Di­methoxy‐2‐phenoxy‐1,3,2‐dioxaphosphorinane 2‐oxide

In the title compound, C₁₁H₁₅O₆P, the six‐membered dioxa­phospho­rinane ring of the cyclic phosphate triester exists in a distorted chair conformation, with the phenoxy group in an axial position. The phenyl ring and both methoxy groups are in a trans–gauche orientation with respect to the 1,3,2‐di­oxa­phospho­rinane ring. In the phosphate group, a significant deformation from the ideal tetrahedral shape is observed. The crystal structure is stabilized by a three‐dimensional network of C—H⋯O interactions.     

Comparison of the effectiveness of epoxy cure accelerators using a fluorescent molecular probe

A simple optical method for quantitative comparison of the effectiveness of epoxy cure accelerators, used for speeding up the crosslinking process of epoxy resins with cyclic anhydrides, is described. Fluorescent molecular probes and a miniature fiber optic spectrometer have been applied for measurement of the cure kinetics of a model epoxy resin/anhydride composition in the presence of various cure accelerators. A quantitative index of accelerator performance has been determined for several of the most common accelerators.