Novel Sorbent and Solvent Combination for QuEChERS Soil Sample Preparation for the Determination of Polycyclic Aromatic Hydrocarbons by Gas Chromatography–Mass Spectrometry

Polycyclic aromatic hydrocarbons (PAHs) represent priority contaminants, and the development of fast, reliable and accurate methods for their determination is of essential importance. The soil is a part of the environment which easily accumulates PAHs, making them available for transport to the air and water over long time periods and by plants through the food chain to humans. The aim of present study was to introduce a novel sorbent to the quick, easy, cheap, effective, rugged, and safe technique for soil sample preparation for the determination of 16 European Union priority PAHs by gas chromatography–mass spectrometry. Two solvent systems, 2:1 (v/v) hexane:acetone and ethyl acetate, were investigated in combination with five clean-up sorbents [Primary secondary amine (PSA), C18, florisil, clinoptilolite, and diatomaceous earth] in this study. The highest overall recovery of the method was achieved by the combination of hexane:acetone with clinoptilolite (recoveries of 70–110%) with limits of detection in the range of 0.60–1.53?µg?kg^?1. The analysis of 20 soil samples from Ni?, Serbia resulted in the identification of 11 samples with concentration greater than the values prescribed by law. The ratios of phenanthrene/anthracene and fluoranthene/pyrene were used to elucidate the origin of the PAHs as pyrolytic.     

Simplex space‐time meshes in two‐phase flow simulations

In this paper, we present the numerical solution of 2‐phase flow problems of engineering significance with a space‐time finite element method that allows for local temporal refinement. Arbitrary temporal refinement is applied to preselected regions of the mesh and is governed by a quantity that is part of the solution process, namely, the interface position in 2‐phase flow. Because of local effects such as surface tension, jumps in material properties, etc, the interface can in general be considered a region that requires high flexibility and high resolution, both in space and in time. The new method, which leads to tetrahedral (for 2D problems) and pentatope (for 3D problems) meshes, offers an efficient yet accurate approach to the underlying 2‐phase flow problems.     

Highly luminescent half-lantern cyclometalated platinum(II) complex: synthesis, structure, luminescence studies, and reactivity

The half-lantern compound [{Pt(bzq)(μ-C(7)H(4)NS(2)-κN,S)}(2)]·Me(2)CO (1) was obtained by reaction of equimolar amounts of potassium 2-mercaptobenzothiazolate (KC(7)H(4)NS(2)) and [Pt(bzq)(NCMe)(2)]ClO(4). The Pt(II)···Pt(II) separation in the neutral complex [{Pt(bzq)(μ-C(7)H(4)NS(2)-κN,S)}(2)] is 2.910 (2) ?, this being among the shortest observed in half-lantern divalent platinum complexes. Within the complex, the benzo[h]quinoline (bzq) groups lie in close proximity with most C···C distances being between 3.3 and 3.7 ?, which is indicative of significant π-π interactions. The reaction of 1 with halogens X(2) (X(2) = Cl(2), Br(2), or I(2)) proceeds with a two-electron oxidation to give the corresponding dihalodiplatinum(III) complexes [{Pt(bzq)(μ-C(7)H(4)NS(2)-κN,S)X}(2)] (X = Cl 2, Br 3, I 4). Their X-ray structures confirm the retention of the half-lantern structure and the coordination mode of the bzq and the bridging ligand μ-C(7)H(4)NS(2)-κN,S. The Pt-Pt distances (Pt-Pt = 2.6420(3) ? 2, 2.6435(4) ? 3, 2.6690(3) ? 4) are shorter than that in 1 because of the Pt-Pt bond formation. Time dependent-density functional theory (TD-DFT) studies performed on 1 show a formal bond order of 0 between the metal atoms, with the 6p(z) contribution diminishing the antibonding character of the highest occupied molecular orbital (HOMO) and being responsible for an attractive intermetallic interaction. A shortening of the Pt-Pt distance from 2.959 ? in the ground state S(0) to 2.760 ? in the optimized first excited state (T(1)) is consistent with an increase in the Pt-Pt bond order to 0.5. In agreement with TD-DFT calculations, the intense, structureless, red emission of 1 in the solid state and in solution can be mainly attributed to triplet metal-metal-to-ligand charge transfer ((3)MMLCT) [dσ*(Pt-Pt) → π*(bzq)] excited states. The high quantum yields of this emission measured in toluene (44%) and solid state (62%) at room temperature indicate that 1 is a very efficient and stable (3)MMLCT emitter, even in solution. The high luminescence quantum yield of its red emission, added to its neutral character and the thermal stability of 1, make it a potential compound to be incorporated as phosphorescent dopant in multilayer organic light-emitting devices (OLEDs).     

Stereochemistry modulates the catalytic hydrogenolysis of nitrile-substituted cyclopropanes

The study of Raney-Ni catalyzed chemo- and regioselective hydrogenolysis of diastereomeric nitrile-substituted spirocyclopropyloxindoles is presented. The chemoselectivity outcome of the reaction is remarkably influenced by the relative stereochemistry of the nitrile-substituted spirocyclopropyloxindoles. Chemo- and high regioselective cyclopropane ring-opening occurs from the syn diastereomers to give the corresponding 3-propylacetamide derivatives. X-ray crystallographic studies together with DFT model chemistry calculations indicate that chemo- and regioselectivity are directly dependent on the bond length asymmetry of the cyclopropane ring.     

Synthesis of copolymer-stabilized silver nanoparticles for coating materials

Silver ions being less toxic than silver nanoparticles, a more safe material can be obtained to be used as antimicrobial coating. This can be achieved by using thiol chemistry and covalently attach the silver nanoparticles in the coating. Our aim is to produce a coating having antimicrobial properties of silver ions but with the silver nanoparticles firmly attached in the coating. Here, we present a way to produce silver nanoparticles that can be used as a component in a coating or as such to produce an antimicrobial coating. The silver nanoparticles presented here are stabilized by a copolymer (poly(butyl acrylate–methyl methacrylate)) that is soft and has well-known good film-producing properties. The reversible addition-fragmentation chain transfer radical polymerization technique used to prepare the polymers provides conveniently a thiol group for effective binding of the silver nanoparticles to the polymers and thus to the coating.     

Synthesis,Characterization and X-Ray Crystal Structure of the Tri Aqua (3-Hydroxy-5-Hydroxymethyl-2-Methylpyridine-4-Carboxaldehyde-3-Methylisotiosemicarbazone: k<Superscript>3</Superscript>, O<Superscript>3</Superscript>, N<Superscript>7</Superscript>, N<Superscript>10</Superscript>) Ni(II) Nitrate

Abstract  

The title complex triaqua (3-hydroxy-5-hydroxymethyl-2-methylpyridine-4-carboxaldehyde-3-methylisothiosemicarbazone-k³,O³,N⁷,N¹⁰)Ni(II) nitrate ([Ni(PLITSC)(H₂O)₃](NO₃)₂, 1) represents the second transition metal complex incorporating an isothiosemicarbazide-pyridoxal based Schiff base that has been crystallographically characterized. Complex 1 crystallizes in a P21/n space group, with lattice constants: a = 11.2254(1) ?, b = 12.9941(2) ?, c = 12.8663(2), β = 96,7713(5)°, V = 1863.64(4) ?³, Z = 4, F(000) = 1016, R ₁ = 0.0681, wR ₂ = 0.1201. The central Ni(II) cation is found in a six-coordinate octahedral geometry formed by the tridentate Schiff base ligand PLITSC and three water molecules. The identity of 1 was further confirmed by elemental analysis, IR spectra, and conductometric and magnetochemical measurements.     

(3, 3)-Ary Differential Rings

The main purpose of this paper is to introduce the concept of (3, 3)-ary differential rings as a generalization of differential rings. Then we study ideals, prime ideals, radical and nil ideals of them. Finally, we give a construction of hyperstructures determined by (3, 3)-ary differential rings.     

Hydrolysis of phosphotriesters: a theoretical analysis of the enzymatic and solution mechanisms

A theoretical study on the alkaline hydrolysis of paraoxon, one of the most popular organophosphorus pesticides, in aqueous solution and in the active site of Pseudomonas diminuta phosphotriesterase (PTE) is presented. Simulations by means of hybrid quantum mechanics/molecular mechanics (QM/MM) potentials show that the hydrolysis of paraoxon takes place through an A(N)D(N) or associative mechanism both in solution and in the active site of PTE. The results correctly reproduce the magnitude of the activation free energies and can be used to rationalize the observed kinetic isotope effects (KIEs) for the hydrolysis of paraoxon in both media. Enzymatic hydrolysis of O,O-diethyl p-chlorophenyl phosphate, a phosphotriester having a leaving group with higher pK(a) than paraoxon, was also simulated. Hydrolysis of this phosphotriester by PTE follows a A(N)+D(N) mechanism with a pentacoordinate intermediate. Moreover, the leaving group of this new substrate coordinates to one of the zinc ions of the bimetallic active site in order to stabilize the large negative charge developed on the oxygen atom of the leaving group when the P-O bond is broken in the products state. To accommodate this new ligand in the coordination shell, carbamylated Lys169 must be displaced from one zinc ion to the other, which in turn affects the acidity of Asp301, a residue originally bound to the second zinc ion. This ability to displace some of the ligands of the coordination shell of the zinc centers would explain the promiscuity of this enzyme, which is capable of catalyzing hydrolysis of different substrate by means of different mechanisms.     

Increase of photoinduced birefringence in a new type of anisotropic nanocomposite: azopolymer doped with ZnO nanoparticles

We report a significant increase of about 50% of the photoinduced birefringence in nanocomposite films of azopolymers doped with ZnO nanoparticles compared with samples made from nondoped azopolymers. This increase is most pronounced at small concentrations of the nanoparticles of 0.5% and for the amorphous polymers used in our study. We observe also an improvement of the response time of more than 25% in some of the polymers, which allows for faster and more effective polarization optical recording.     

EPR Investigation of Exchange Interactions Between Neodymium Ions in {[Nd2(α-C4H3OCOO)6(H2O)2]} n

Electron paramagnetic resonance (EPR) of a new compound {[Nd₂(α-C₄H₃OCOO)₆(H₂O)₂]} _n composed of Nd³⁺–Nd³⁺ dimers is reported. The anisotropy parameters of the spin–spin interaction are determined by fitting experimental and simulated spectra in X- and Q-bands. It is shown that the anisotropy of the exchange interaction gives the main contribution to the anisotropy of the spin–spin interaction. The observed anisotropy disagrees with the expected in the model of the isotropic exchange interaction between real spins. A feature of the EPR spectrum not described by the model of the isolated Nd–Nd dimers and reflecting the magnetization transfer between dimers is detected. The magnetization transfer due to both the relaxation transitions and the interdimer interaction is considered.