Sorption of As(V) on aluminosilicates treated with Fe(II) nanoparticles

Adsorption of arsenic on clay surfaces is important for the natural and simulated removal of arsenic species from aqueous environments. In this investigation, three samples of clay minerals (natural metakaoline, natural clinoptilolite-rich tuff, and synthetic zeolite) in both untreated and Fe-treated forms were used for the sorption of arsenate from model aqueous solution. The treatment of minerals consisted of exposing them to concentrated solution of Fe(II). Within this process the mineral surface has been laden with Fe(III) oxi(hydroxides) whose high affinity for the As(V) adsorption is well known. In all investigated systems the sorption capacity of Fe(II)-treated sorbents increased significantly in comparison to the untreated material (from about 0.5 to >20.0 mg/g, which represented more than 95% of the total As removal). The changes of Fe-bearing particles in the course of treating process and subsequent As sorption were investigated by the diffuse reflectance spectroscopy and the voltammetry of microparticles. IR spectra of treated and As(V)-saturated solids showed characteristic bands caused by Fe(III)SO(4), Fe(III)O, and AsO vibrations. In untreated As(V)-saturated solids no significant AsO vibrations were observed due to the negligible content of sorbed arsenate.     

Tandem Michael addition/amino-nitrile cyclization from 2-formyl-1,4-DHP in the synthesis of novel dihydroindolizine-based compounds

A simple and efficient methodology for the synthesis of a small library of substituted indolizines with different degrees of saturation starting from the racemic 2-formyl-1,4-DHP reagent was described. The large synthetic possibilities of this reagent as well as of its Knoevenagel corresponding 2-dicyanovinyl-1,4-DHP reagent were investigated using four kinds of activated methylenes as nucleophiles. The key step of the sequential reaction was based on the highly diastereoselective tandem Michael addition/intramolecular amino-nitrile cyclization catalyzed by an organic base, which resulted in the formation of 1,7-dihydroindolizines in a diastereoselective manner. The process seems to be a straightforward one and can be extended to numerous active methylenes such as malononitrile, 1,3-diketones, and alkyl acetoacetates. The 1,3-hydrogen shift of partially hydrogenated indolizines was accomplished easily with a base at room temperature, giving rise to the corresponding 7,8-dihydroindolizines in very good yields. Interestingly, when the active methylene bears a leaving group, the latter process could not be accomplished because a rare cis-elimination of phenylsulfinic acid and nitrous acid preceded the hydrogen shift. The resulting 1,7-dihydroindolizines bearing an exo-methylene group at C1 were not isolated in all cases, as they turned rapidly to indolizines as the thermodynamically more stable products. During these investigations, oxidization of 1,7-dihydroindolizines with CuCl(2) resulted in the formation of polysubstituted pyridines. Also, the epimerization of certain 1,7-dihydroindolizines was evidenced in the solution studied by NMR spectroscopy, whereas in the solid state, they existed only in a unique form as shown by X-ray diffraction analysis of a representative structure. Finally, all products reported herein bear a primary amine and a nitrile function crucial for further transformations. These include the introduction of various pharmacophore groups at either NH(2) or CN groups as well as at both groups at the same time to access the more elaborated indolizines fused to N- or N,N-heterocycles.     

Analytical performances of validated chemiluminescent enzyme immunoassays to detect N-methylcarbamate pesticides

In the present work, enzyme-linked immunosorbent assays (ELISAs) with chemiluminescent detection for the determination of carbofuran, carbaryl and methiocarb were developed and the analytical parameters of these assays were compared with those of ELISAs with colorimetric detection. Both were conjugate-coated formats based on identical monoclonal antibodies and homologous protein conjugates. In comparison with colorimetric ELISA, the ability of the chemiluminescent reagents to detect lower concentrations of horseradish peroxidase allowed to decrease the optimal antibody and conjugate concentrations and to reach better analytical parameters. The experimental comparison of the analytical performance of the ELISAs was carried out by analysing extracts of apple-strawberry baby food and simply diluted fruit juices, both spiked at different concentration levels with the above mentioned pesticides. Recovery values for both ELISAs were around 100% and no matrix effects were observed when fruit juices were diluted 1:20 or more. Results obtained by ELISAs correlated well, both in terms of accuracy and precision, with those obtained by a liquid chromatography-electrospray mass spectrometry (LC/ESI/MS/MS) analysis, used as reference method to validate the immunoassays results. The limits of detection reached by using the chemiluminescent assay were 0.03, 0.007 and 0.004 ng ml⁻¹ for carbofuran, carbaryl and methiocarb, respectively.     

Comparison of a new high‐resolution monolithic column with core‐shell and fully porous columns for the analysis of retinol and α‐tocopherol in human serum and breast milk by ultra‐high‐performance liquid chromatography†

The reduction of analysis time, cost, and improvement of separation efficiency are the main requirements in the development of high‐throughput assay methods in bioanalysis. It can be achieved either by ultra‐high‐performance liquid chromatography (UHPLC) using stationary phases with small particles (<2 μm) at high back pressures or by using opposite direction—monolithic stationary phases with low back pressures. The application of new types of monolithic stationary phases for UHPLC is a novel idea combining these two different paths. The aim of this work was to test the recently introduced second‐generation of monolithic column Chromolith® HighResolution for UHPLC analysis of liposoluble vitamins in comparison with core‐shell and fully porous sub‐2 μm columns with different particle sizes, column lengths, and shapes. The separation efficiency, peak shape, resolution, time of analysis, consumption of mobile phase, and lifetime of columns were calculated and compared. The main purpose of the study was to find a new, not only economical option of separation of liposoluble vitamins for routine practice.     

Coordination bonding in dicopper and dichromium tetrakis(μ-acetato)-diaqua complexes: Nature,strength, length,and topology

Geometry optimization, energetics, electronic structure, and topology of electron density of dicopper ( I ) and dichromium ( II ) tetrakis(μ-acetato)-diaqua complexes are studied focusing on the metal–metal interactions. The performance of broken symmetry (BS) single-determinant ab initio (Hartree–Fock, Møller–Plesset perturbation theory to the second and third orders, coupled clusters singles and doubles) and density functional theory (BLYP, B3LYP, B3LYP-D3, B2PLYP, MPW2PLYP) methods is compared to multideterminant ab initio (CASSCF, NEVPT2) methods as well as to the multipole model of charge density from a single-crystal X-ray diffraction experiment (Herich et al., Acta Cryst. 2018, B74, 681–692). In vacuo DFT geometry optimizations (improper axial water ligand orientation) are compared against the periodic ones. The singlet state is found to be energetically preferred. J coupling of ( I ) becomes underestimated for all ab initio methods used, when compared to experiment. It is concluded that the strength of the direct M─M interactions correlates closely with the J coupling magnitude at a given level of theory. The double potential well character of (II) and of the dehydrated form of (II) are considered with respect to the Cr─Cr distance. The physical effective bond order of the metal–metal interaction is small (below 0.1 e) in ( I ) and moderate (0.4 e) in ( II ). The CASSCF results overestimate the electron density of the metal–metal bond critical point by 20% and 50% in ( I ) and ( II ), respectively, when compared to the multipole model. © 2019 Wiley Periodicals, Inc.     

Design and development of functionalized cyclometalated ruthenium chromophores for light-harvesting applications

The syntheses and the electrochemical spectroscopic properties of a suite of asymmetrical bistridentate cyclometalated Ru(II) complexes bearing terminal triphenylamine (TPA) substituents are reported. These complexes, which contain structural design elements common to both inorganic and organic dyes that exhibit superior power conversion efficiencies in the dye-sensitized solar cell (DSSC), are broadly formulated as [Ru(II)(L-2,5'-thiophene-TPA-R(1))(L-R(2))](+) [L = tridentate chelating ligand (e.g., 2,2':6',2'-terpyridine (tpy); deprotonated forms of 1,3-di(pyridin-2-yl)benzene (Hdpb) or 6-phenyl-2,2'-bipyridine (Hpbpy)); R(1) = -H, -Me, -OMe; R(2) = -H, -CO(2)Me, -CO(2)H]. The following structural attributes were systematically modified for the series: (i) electron-donating character of the terminal substituents (e.g., R(1) = -H, -Me, -OMe) placed para to the amine of the "L-2,5'-thiophene-TPA-R(1)" ligand framework; (ii) electron-withdrawing character of the tridentate chelate distal to the TPA-substituted ligand (e.g., R(2) = -H, -CO(2)Me, -CO(2)H); and (iii) position of the organometallic bond about the Ru(II) center. UV-vis spectra reveal intense and broad absorption bands arising from a collection of metal-to-ligand charge-transfer (MLCT) and TPA-based intraligand charge-transfer (ILCT) transitions that, in certain cases, extend beyond 800 nm. Electrochemical data indicate that the oxidative behavior of the TPA and metal chelate units can be independently modulated except in cases where the anionic phenyl ring is in direct conjugation with the TPA unit. In most cases, the anionic character of the cyclometalating ligands renders a metal-based oxidation event prior to the oxidation of the TPA unit. This situation can, however, be reversed with an appropriately positioned Ru-C bond and electron-rich R(1) group. This finding is important in that this arrangement confines the highest occupied molecular orbital (HOMO) to the TPA unit rather than the metal, which is optimal for sensitizing TiO(2); indeed, a remarkably high power conversion efficiency (η) in the DSSC (i.e., 8.02%) is measured for the TPA-substituted pbpy(-) chelate where R(1) = -OMe. These results provide a comprehensive strategy for improving the performance of bistridentate Ru sensitizers devoid of NCS(-) groups for the DSSC.     

Advanced liquid chromatography/mass spectrometry profiling of anthocyanins in relation to set of red wine varieties certified in Czech Republic

Hyphenation of micro-liquid and ultra-performance liquid chromatography with a hybrid (QqTOF) tandem mass spectrometry was studied from the viewpoint of their applicability for monitoring of anthocyanin dyes in various cultivars and different vintages of red wine. After appropriate optimization both techniques proved to be suitable for this task. UHPLC system provided lower LOD and LOQ values as well as higher productivity and precision of retention parameters and peak areas with respect to micro-LC method. On the other hand, micro-LC method offers significant savings of mobile phase, less contamination of ion source of mass spectrometer and makes the nebulization process in electrospray much easier. In combination with principal component analysis (PCA), the method allows to elucidate long-term relations in a complete set of certified red wine cultivars grown in South Moravia (certified in Czech Republic until year 2005). Among the studied varieties Rubinet exhibit a specific anthocyanin profile. Especially interesting is a high content of 3-coumaroylglucoside-5-glucosides of malvidin and peonidin. Those dyes can be used as markers of artificial color enhancement. Principal component analysis applied to data processed with regard to enzymatic activity markedly facilitate classification among varieties. This approach allows resolution of teinturiers, variety Blaufränkish and partial classification of other varieties.     

Purine Scaffold Effect on Fluorescence Properties of Purine-Hydroxyquinolinone Bisheterocycles

The fluorescence properties of bisheterocyclic compounds that contain purine and the 3-hydroxyquinolin-4(1H)-one skeleton connected with an aliphatic spacer of a different length/structure (3HQP) were examined. It was found that the introducing of the spacer-purine scaffold led in the comparison to 3HQs themselves to (1) the possibility of the effectual excitation in the wider range of excitation wavelengths, moreover, some derivatives can be excited at relatively high wavelengths around 400 nm, (2) the lowering of the quantum yield and (3) the slight longer wavelength shift of the dual emission spectra. Tested organic solvents did not affect significantly the 3HQP fluorescence properties. The characters of emission spectra as well as the quantum yields of 3HQPs were notably influenced by the ratio of water and DMSO in their composed mixture applied as a solvent. With increasing water content in the mixture both I₁/I₂ and the quantum yield decreased.     

Ni Oxidation State and Ligand Saturation Impact on the Capability of Octaazamacrocyclic Complexes to Bind and Reduce CO2

Two 15-membered octaazamacrocyclic nickel(II) complexes are investigated by theoretical methods to shed light on their affinity forwards binding and reducing CO₂. In the first complex ¹[Ni^IIL]⁰, the octaazamacrocyclic ligand is grossly unsaturated (π-conjugated), while in the second ¹[Ni^IILH]²⁺ one, the macrocycle is saturated with hydrogens. One and two-electron reductions are described using Mulliken population analysis, quantum theory of atoms in molecules, localized orbitals, and domain averaged fermi holes, including the characterization of the Ni-C_CO2 bond and the oxidation state of the central Ni atom. It was found that in the [NiLH] complex, the central atom is reduced to Ni⁰ and/or Ni^I and is thus able to bind CO₂ via a single σ bond. In addition, the two-electron reduced ³[NiL]²⁻ species also shows an affinity forwards CO₂.     

Sorption of anthropogenic radionuclides onto river sediments and suspended solids: dependence on sediment composition

Journal of Radioanalytical and Nuclear Chemistry - The purpose of the study is to explore the sorption behaviour of anthropogenic radionuclides in the Vltava River catchment in the Czech Republic,...