Velocity Measurements of a Free-Surface Turbulent Flow Penetrating a Porous Medium Composed of Uniform-Size Spheres

We present a laboratory experimental investigation of the interaction between the turbulent flow in an open channel and the turbulent flow within its very permeable bed. The bed was composed of uniform-size spheres packed in a cubic pattern. Fluid velocities were measured by Particle Image Velocimetry (PIV), which allowed us to investigate the spatial distribution of the time-averaged flow properties in the zone where they are strongly affected by the geometry of the rough bed. We investigate the effect of bed porosity on these flow properties by comparing the results of two experimental configurations: one with an impermeable bed composed of a single layer of spheres and another with a permeable bed composed of five layers. For the latter case, PIV measurements of velocities were also carried out inside two pores adjacent to the bed surface. This data provides an insight into the mechanisms of momentum transfer between the turbulent open channel flow and the turbulent flow within its very permeable bed.     

ESI‐MS studies of palladium (II) complexes with 1‐(p‐toluenesulfonyl)cytosine/cytosinato ligands

The mononuclear complex Pd(1‐TosC‐N3)₂Cl₂ (2) containing 1‐(p‐toluenesulfonyl)cytosine (1) as a ligand, as well as dinuclear complexes Pd₂(1‐TosC^?‐N3,N4)₄ (3) and Pd₂(1‐TosC^?‐N3,N4)₂DMSO₂Cl₂ (4) containing the ligand anion (1‐TosC^?), was mass analyzed by electrospray ionization ion trap MS/MS and high resolution MS. Complexes 3 and 4 were obtained by recrystallization of 2 from DMF and DMSO, respectively. The behavior of complex 2 in different solutions was monitored by electrospray ionization mass spectrometry (ESI‐MS). Under the applied ESI‐MS conditions, complex 2 in methanol reorganized itself dominantly as new complex 3 and the solvent did not coordinate the formed species. In H₂O/DMSO, CH₃CN/DMSO and CH₃OH/DMSO solutions, complex 2 formed several new species with solvent molecules involved in their structure, e.g. complex 4 was formed as the major product. The newly formed species were also examined by LC‐MS‐DAD, confirming the solvent induced reorganization and the solution instability of complex 2. Copyright © 2009 John Wiley & Sons, Ltd.     

A study of trace element contamination in river sediments in Serbia using microwave-assisted aqua regia digestion and multivariate statistical analysis

The aim of this study was the evaluation of the trace element contamination level in sediments of the most important rivers in Serbia and their tributaries. The determination of the aqua regia soluble contents of 12 micro- and macro-elements (Ca, Cd, Co, Cr, Cu, Fe, Mn, Pb, Ni, Zn, Be and V) in sediments was developed by the microwave digestion technique combined with inductively coupled plasma atomic emission spectrometry. Correlation analysis and principal component analysis distinguishes factors of lithogenic and anthropogenic origins. The Fe, Mn, Be and V contents are controlled by a regional lithogenic high background factor, while Cd, Cr, Pb, Ni, Zn and Cu are recognized as tracer of pollution. For Co, mixed sources from both lithogenic and anthropogenic inputs were evidenced.The investigated sediment of the major rivers and their tributaries in Serbia showed high concentrations of metals, especially of Cd, Pb, Cu and Zn, which may cause serious environmental impacts. Rivers which flow into the Danube from its entrance into Serbia significantly influence the chemical load of the water and sediments.The experimental study was conducted using two BCR standard reference materials. The calculated accuracy and precision confirmed the good performance of the adopted procedures.     

Simultaneous potentiometric determination of cationic and ethoxylated nonionic surfactants in liquid cleaners and disinfectants

A sensitive potentiometric surfactant sensor based on a highly lipophilic 1,3-didecyl-2-methyl-imidazolium cation and a tetraphenylborate (TPB) antagonist ion was used as the end-point detector in ion-pair potentiometric surfactant titrations using sodium TPB as a titrant. Several analytical and technical grade cationic and ethoxylated nonionic surfactants (EONS) and mixtures of both were potentiometrically titrated.The sensor showed satisfactory analytical performances within a pH range of 3-10 and exhibited satisfactory selectivity for all CS and EONS investigated. Ionic strength did not influence the titration except at 0.1 M NaCl, in which a slight distortion of the second inflexion corresponded with the nonionic surfactant.Two-component combinations of four CS and three EONS were potentiometrically titrated using the sensor previously mentioned as the end-point detector. The quantities of the surfactants varied between 2 and 6 μmol for CS and 2.50 and 7.50 μmol for EONS. The known addition methodology was used for determination of the surfactant with considerably lower concentration in the mixture.Three commercial products containing cationic surfactants as disinfectants and nonionic surfactants were potentiometrically titrated, and the results for both type of surfactants were compared with those obtained with standard conventional methods.     

Di­iodo(3,4,5,6‐tetrahydropyrimidin­ium‐2‐thiol­ato‐S)­mercury(II)

The reaction of 3,4,5,6‐tetrahydropyrimidine‐2‐thione (H₄py­mtH) with mercury(II) iodide in methanol in a 1:1 molar ratio resulted in the formation of single crystals of the title compound, [Hg(C₄H₈N₂S)I₂]. The Hg atom is coordinated by one S atom from H₄pymtH at 2.456 (2) Å and by two I atoms at distances of 2.6872 (7) and 2.7044 (6) Å, and has a characteristic deformed trigonal coordination geometry. The molecule has crystallographic m symmetry but the Hg atom is disordered above and below the mirror plane.     

New Method for the Synthesis of 2‐Aza‐1,3‐Butadienes

2‐Aza‐1,3‐butadienes have been synthesized from carbonyl compounds and 1,1,1,3,3,3‐hexamethyl‐disilazane in the presence of cobalt‐containing catalysts. The best yields (up to 95%) were achieved in the case of aldehydes branched in the α-position and 2-methylcyclohexanone. In the case of two α,β‐unsaturated ketones, pyridine derivatives were found as the main products.     

A new complex of HgBr2 and pyrimidine‐2‐thione: (pyrimidine‐2‐thionato‐κS)(pyrimidinium‐2‐thionato‐κS)mercury(II) tetrabromomercury(II)

The title compound, [Hg(C₄H₄N₂S)(C₄H₃N₂S)]₂[HgBr₄], con­sists of [Hg(pymt)(pymtH)]⁺ complex cations (pymtH is pyrimidine‐2‐thione) lying across twofold rotation axes in space group Fddd, with linearly coordinated mercury at an Hg—S distance of 2.357 (3) Å, and [HgBr₄]²⁻ anions lying at sites of 222 symmetry. The Hg atom is additionally coordinated by two N and two Br atoms, forming a 2+4 effective coordination sphere. The protonated ligand is connected via N—H⋯N hydrogen bonds to the neighbouring unprotonated ligand, thus forming infinite chains of cations.     

Synthesis and Structure of cis-Dioxo(3-Methoxysalicylaldehyde 4-Methylthiosemicarbazonato-N,O,S)(γ-Picoline-N)Molybdenum(VI)

Abstract  Red crystals of cis-dioxo(3-methoxysalicylaldehyde 4-methylthiosemicarbazonato-N,O,S)(γ-picoline-N)molybdenum(VI), [MoO₂L(γ-pic)], [L²⁻=CH₃OC₆H₄(O)CH=NN=C(S)NHCH₃, 3-methoxysalicylaldehyde 4-methylthiosemicarbazonato] were prepared by the reaction of [MoO₂L] _n with γ-picoline in dry methanol. The title compound crystallized in the monoclinic space group P2₁/n, a = 6.7984(7) ?, b = 15.9760(12) ?, c = 17.1466(14) ?, β = 93.613(8)°, V = 1858.6(3) ?³, Z = 4. The coordination geometry around the molybdenum center is distorted octahedral with the tridentate thiosemicarbazonato ligand (L²⁻) bonded meridionally to the [MoO₂]²⁺ core. The sixth coordination site is occupied by a weakly bound γ-picoline molecule. The adjacent molecules are joined by the N–H···O hydrogen bonds between their amino and methoxy groups thus forming infinite molecular chains. The three-dimensional solid-state structure is achieved by the additional C–H···O, C–H···π and van der Waals interactions. Graphical Abstract  In the title compound, [MoO₂L(γ-pic)], the tridentate thiosemicarbazonato ligand (L²⁻) is meridionally bound to the [MoO₂]²⁺ core, while a molecule of γ-picoline completes the distorted octahedral coordination around the metal atom.      

The Solvent Effect on Composition and Dimensionality of Mercury(II) Complexes with Picolinic Acid

Three new mercury(II) coordination compounds, {[HgCl(pic)]}_n (1), [HgCl(pic)(picH)] (2), and [HgBr(pic)(picH)] (3) (picH = pyridine-2-carboxylic acid, picolinic acid) were prepared by reactions of the corresponding mercury(II) halides and picolinic acid in an aqueous (1) or alcohol–methanol or ethanol (2 and 3) solutions. Two different types of coordination compounds were obtained depending on the solvent used. The crystal structures were determined by the single-crystal X-ray structural analysis. Compound 1 is a one-dimensional (1-D) coordination polymer with mercury(II) ions bridged by chelating and bridging N,O,O′-picolinate ions. Each mercury(II) ion is four-coordinated with a bidentate picolinate ion, a carboxylate O atom from the symmetry-related picolinate ion and with a chloride ion; the resulting coordination environment can be described as a highly distorted tetrahedron. Compounds 2 and 3 are isostructural mononuclear coordination compounds, each mercury(II) ion being coordinated with the respective halide ion, N,O-bidentate picolinate ion, and N,O-bidentate picolinic acid in a highly distorted square-pyramidal coordination environment. Compounds 1–3 were characterized by IR spectroscopy, PXRD, and thermal methods (TGA/DSC) in the solid state and by ¹H and ¹³C NMR spectroscopy in the DMSO solution.