Vortex Shedding: A Review on Flat Plate

Flat plates, both single and in tandem or side by side arrangement, are widely used in many engineering applications. Despite vast investigations of the flow structures and wakes downstream of these bluff bodies, this unsteady phenomenon yet remains a fundamental issue in many industrial applications. This paper reviews the state of the art concerning the flow over flat plates in different arrangements focusing on plates normal to the flow. Turbulent wake regions are discussed for the flat plates in side by side or tandem arrangement. Numerical studies are reviewed with emphasis on the realized turbulent models. The effect of the chosen turbulence model on the prediction of the wake region is discussed.     

Synthesis and structure of iron(iii) diamine-bis(phenolate) complexes

The structures and properties of six new iron(iii) diamine-bis(phenolate) complexes are reported. Reaction of anhydrous FeX(3) salts (where X = Cl or Br) with the diprotonated tripodal tetradentate ligands 2-pyridylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)[L(1)], and N,N-dimethyl-N',N'-bis(2-methylene-4-methyl-6-tert-butylphenol)ethylenediamine, H(2)[L(2)], produces the trigonal bipyramidal iron(iii) complexes, [L(1)]FeCl , [L(1)]FeBr , [L(2)]FeCl and [L(2)]FeBr . Reaction of FeX(3) with the related linear tetradentate ligand N,N'-bis(4,6-tert-butyl-2-methylphenol)-N,N'-bismethyl-1,2-diaminoethane, H(2)[L(3)], generates square pyramidal iron(iii) complexes, [L(3)]FeCl and [L(3)]FeBr . Complexes have been characterized using electronic absorption spectroscopy and magnetometry. Single crystal X-ray molecular structures have been determined for complexes 1, 3, 5 and 6.     

preconcentration and determination of amoxicillin and ceftriaxone in hospital sewage using vortex-assisted liquid-phase microextraction based on the solidification of the deep eutectic solvent followed by HPLC–UV

In the present study, a new method for extraction and preconcentration of amoxicillin and ceftriaxone was used in hospitalised sewage samples, called vortex-assisted liquid-phase microextraction based on the solidification of deep eutectic solvent. Samples were analysed by high-performance liquid chromatography–ultraviolet detection after preparation and extraction. In this method, the new deep eutectic solvent is used as the extraction solvent, which is obtained from the combination of 1-decyl-3-methylimidazolium chloride and n-butanoic acid. The important advantages of this novel extraction solvent include material stability, low density and good freezing point near room temperature. Under the optimum conditions, enrichment factors are in the range of 164–172. Repeatability and reproducibility of the method based on seven replicate measurements of 50.0 µg L^?1 of the target analytes in analysed samples were in the range of 2.1–3.5% and 3.8–5.2%, respectively. The limit of detections and linearity are in the range of 0.005–0.10 and 3–600 µg L^?1, respectively. The method was successfully applied for the determination of amoxicillin and ceftriaxone in the real sewage samples. The relative recoveries of sewage samples spiked with amoxicillin and ceftriaxone are 91–107%.     

Protonation Equilibria of Carminic Acid and Stability Constants of Its Complexes with Some Divalent Metal Ions in Aqueous Solution

The dissociation constants of carminic acid (7-D-glucopyronosyl-3,5,6,8-tetra- hydroxy-1-methyl-9,10-dioxo-anthracene-2-carboxylic acid) (CA), together with the stability constants of its Cu(II), Zn(II), Ni(II), Co(II) and Hg(II) complexes, were studied potentiometrically in aqueous medium at 25.0?(1)?°C, and at the ionic background of 0.1?mol?dm^?3 of NaCl, and determined with the SUPERQUAD computer program. It has been observed that carminic acid has five dissociation constants, and for H₅L their values are 3.39?(7), 5.78?(7), 8.35?(7), 10.27?(7), and 11.51?(7). This ligand behaves as a bi-dentate ligand, and the carboxyl and the ortho hydroxy groups of the ligand coordinate to the metal ions. Various metal complexes were produced in solution under the experimental conditions, for each metal ion used, including hydrolyzed species. The species distribution curves of the complexes formed in the solution were calculated and reviewed. The stability of the complexes was found to follow the order: Cu(II) > Zn(II) > Ni(II) > Co(II) > Hg(II).     

Investigation of Solution p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> and Thermodynamic Values of Lamivudine and Pefloxacin Drugs by Ab initio and DFT Methods

In this work we investigate the thermodynamic properties and pK_a value of lamivudine and pefloxacin drugs, in aqueous solutions, by ab initio and density functional theory (DFT) methods at different temperatures. Molecular structures and solute–solvent effects of the anions, cations, and neutral molecules of lamivudine and pefloxacin were studied by the polarizable continuum model (PCM). The calculation was done at the DFT-B3LYP/6-31+G(d) level of theory using Tomasi’s method to analyze the formation of intermolecular hydrogen bonds (IHB) in aqueous solution. The pK_a1 values of lamivudine and pK_a2 values of pefloxacin increase with temperature increase. In contrast, the pK_a1 values of pefloxacin decrease when the temperature increases. Further, the thermodynamic properties of the ionization processes (?H, ?S and ?G) of the drugs in aqueous solution were determined and discussed. The results of this work are in good agreement with the literature data at 298.15 K.     

Biological entities as chemical reactors for synthesis of nanomaterials: Progress,challenges and future perspective

Synthesis of nanomaterials is being gained extensive attention in the fields of chemistry, applied physics, catalysis, drug delivery and the most important in diagnosis and therapeutic applications. Recently, many reports have been published on physical and chemical synthesis of magnetic as well as metallic nanoparticles (NPs) with viable surface functionalization, but still there is a dire need of such strategies that can combine synthetic methodology with stable surface modification found in nature. Synthesis of NPs via biological methods is the possible way to solve these barriers. However, systematized summary and outlooks of NPs synthesis via biological entities with various influencing factors e.g. temperature, pH, concentration of reactants and reaction time has rarely been reported. This review will present the distinct advantages of biological synthesis of NPs over physical and chemical methods. It will also highlight the recent progress on synthesis of NPs via various biological systems i.e. plant, fungus, bacteria, and yeast. Furthermore, it will explain various factors that control the size, shape, and morphology of these NPs. Finally, it would present the future perspectives of green chemistry for the development of nano-science and -biotechnology.     

A Systematic Study of ZnO/CuO Core/Shell Nanostructures Pegylated by Microwave Assistant Reverse Micelles (RM) Method

In this work we synthesized ZnO/CuO nanostructures pegylated by simple and fast microwave method assistant reverse micelles, Reverse micelles protocol creates many advantages in stability, particle size control, morphology, density, loading level, distribution, uniformity, charge and purification. Based on the statistical results ZnO/CuO nanostructures placed in the hydrophilic substrate. The effect of microwave and concentration of surfactant on the surface area, pore diameter and pore volume of the final product was systematically studied using Taguchi technique. ZnO/CuO core/shell pegylated nanostructures, indicating a ZnO as core and CuO as shell and continuous micelles chains around this structures. Products were characterized by UV–Vis spectra, X-ray diffraction, scanning electron microscopy, Dynamic light scattering, Energy-dispersive X-ray spectroscopy, transmission electron microscopy and nitrogen adsorption (i.e. Brunauer–Emmett–Teller surface area analysis).     

Synthesis of enantiopure β-amino alcohols via AKR/ARO of epoxides using recyclable macrocyclic Cr(III) salen complexes

A series of chiral macrocyclic Cr(III) salen complexes 1-8 were synthesized and characterized. These complexes were found to be highly active, regio-, diastereo-, and enantioselective catalysts in aminolytic kinetic resolution (AKR) of racemic trans-epoxides as well as asymmetric ring opening (ARO) of prochiral meso-epoxides with various anilines as nucleophiles at room temperature in 18-24 h. Excellent yields (>99% with respect to the nucleophile) with high enantioselectivity (ee, >99%) of chiral anti-β-amino alcohols was achieved with concomitant recovery of corresponding epoxides in high ee (up to >99%). The complex 1 also catalyzed the ARO of meso-epoxides to provide corresponding syn-β-amino alcohols in high yield (99%) and ee (up to 91%). Due to built-in basic sites in the catalyst, no external base (as an additive) was required to promote AKR and ARO reactions. The catalyst 1 was conveniently recycled several times with retention of its performance. The AKR of trans-stilbene oxide with aniline was successfully demonstrated at relatively higher scale (10 mmol) using the catalyst 1.     

Structural conformation of biomolecules released from temperature-sensitive composite polymer particles – a study by circular dichroism

A conformational study of the biomolecules released from submicron- and micron-sized temperature-sensitive composite polymer particles by decreasing the temperature from 40 to 25 °C was done with circular dichroism and the results were compared with those of the native biomolecules. In almost all cases the biomolecules released retained their native conformational states. Received: 10 April 2001 Accepted: 13 June 2001     

The fate of sulfur-bound hydrogen on formation of self-assembled thiol monolayers on gold: (1)H NMR spectroscopic evidence from solutions of gold clusters

It is demonstrated that thiols can adsorb to gold without losing hydrogen. Dodecyl sulfide-capped gold clusters have been prepared and subjected to ligand exchange reactions in perdeuterated benzene by addition of dodecanethiol and subsequently dodecyl disulfide. It is shown by 1H NMR spectroscopy that dodecanethiol molecules are readily taken up as ligands producing characteristic broad signals corresponding to the alpha-methylene and S-H protons, with chemical shifts close to those found for thiol in solution; these signals are absent in spectra of thiolate-capped clusters. Addition of excess disulfide to such clusters capped with both dialkyl sulfides and thiols leads to the appearance of sharp signals for free dialkyl sulfide and intact thiol. Amounts of thiols up to 50% of the ligand shell are, however, taken up by the clusters under rapid and irreversible loss of hydrogen.