High density cationic polymer brushes from combined “click chemistry” and RAFT‐mediated polymerization

A simple method for preparing cationic poly[(ar‐vinylbenzyl)trimethylammonium chloride)] [poly(VBTAC)] brushes was used by combined technology of “click chemistry” and reversible addition‐fragmentation chain transfer (RAFT) polymerization. Initially, silicon surfaces were modified with RAFT chain transfer agent by using a click reaction involving an azide‐modified silicon wafer and alkyne‐terminated 4‐cyanopentanoic acid dithiobenzoate (CPAD). A series of poly(VBTAC) brushes on silicon surface with different molecular weights, thicknesses, and grafting densities were then synthesized by RAFT‐mediated polymerization from the surface immobilized CPAD. The immobilization of CPAD on the silicon wafer and the subsequent polymer formation were characterized by X‐ray photoelectron spectroscopy, water contact angle measurements, grazing angle‐Fourier transform infrared spectroscopy, atomic force microscopy, and ellipsometry analysis. The addition of free CPAD was required for the formation of well‐defined polymer brushes, which subsequently resulted in the presence of free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. In addition, by varying the polymerization time, we were able to obtain poly(VBTAC) brushes with grafting density up to 0.78 chains/nm² with homogeneous distributions of apparent needle‐like structures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

CHEMICAL INVESTIGATIONS ON SOME HYPERICUM SPECIES GROWING IN TURKEY-I

The chemical composition of five taxa of the genusHypericumL. obtained from herbarium specimens has been investigated.Namely, H. adenotrichum Spach(endemic),H. calycinumL.,H. cerastoides(Spach) Robson,H. montbretiiSpach, andH. perforatumL. were subjected to microdistillation to isolate the volatile compounds, which were analyzed by GC/MS.     

Determination of copper traces in water samples by flow injection-flame atomic absorption spectrometry using a novel solidified floating organic drop microextraction method

A simple, rapid and inexpensive solidified floating organic drop microextraction (SFODME) and flow injection flame atomic absorption spectrometric determination (FI-FAAS) method for copper were developed. 3-amino-7-dimethylamino-2-methylphenazine (Neutral red, NR) was used as the complexing agent. Several factors affecting the microextraction efficiency, such as, pH, NR and sodium dodecylbenzenesulfonate (SDBS) concentration, extraction time, stirring rate, and temperature were investigated and optimized. Under optimized experimental conditions an enrichment factor of 541 was obtained for 100 mL of sample solution. The calibration graph was linear in the range of 0.5–20.0 ng mL^{− 1} and the limit of detection (3 s) was 0.18 ng mL^{− 1}, the limit of quantification (10 s) was 0.58 ng mL^{− 1}. The relative standard deviation (RSD) for 10 replicate measurements of 10 ng mL^{− 1} copper was 2.7%. The developed method was successfully applied to the extraction and determination of copper in different certified reference materials (Estuarine water, Slew 3 and fortified water, TM 23.2) and real water samples and satisfactory results were obtained.     

The use of gold nanoparticles as an effective modifier for the determination of arsenic and antimony by electrothermal atomic absorption spectrometry

Gold nanoparticles (AuNPs) were used as a new chemical modifier for the determination of arsenic and antimony in salt solutions by electrothermal atomic absorption spectrometry. The AuNPs were prepared by reducing chloroauric acid with sodium citrate. The effects of pyrolysis and atomization temperatures, the amounts of interferents and modifier on the sensitivities of arsenic and antimony were investigated. As and Sb remain in the graphite tube up to 1,100°C, which is sufficient for the determination of the two metals in certified reference materials and spiked sea water samples within a 95% confidence level with low RSD (<10%). The detection limits (N?=?10 at 3??) for As and Sb in sea water are 2.3???g?L^-1 and 3.0???g?L^-1, respectively. Almost no background as well as a blank value was detected for AuNPs.

Essential oil composition of endemic Tanacetum zahlbruckneri (Nab.) and Tanacetum tabrisianum (Boiss.) Sosn. and Takht. from Turkey

In this study, water-distilled essential oils from the flowers of Tanacetum zahlbruckneri and flowers and stems of Tanacetum tabrisianum from Turkey were analysed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The flower oil of T. zahlbruckneri was characterised by the sesquiterpenes germacrene D (29.7%) and spathulenol (12%). Flower (A) and stem (B) oil of T. tabrisianum was characterised by 1,8-cineole: 17.6% (A), 22.5% (B), hexadecanoic acid: 10.3% (A), 8% (B), decanoic acid: 5.8% (A) and trans-linalooloxide acetate: 5.3% (A), 4% (B). Unlike a previous report on the essential oil composition of T. tabrisianum, in this study a 1,8-cineole and hexadecanoic acid-rich oil with a low percentage of caryophyllene oxide and spathulenol was obtained. The composition of the essential oil of endemic T. zahlbruckneri was investigated for the first time.     

Korovkin type approximation theorem via Ka−convergence on weighted spaces

In this paper, we study the Korovkin type approximation theorem for K_a‐ convergence, which is an interesting convergence method on weighted spaces. We also study the rate of K_a?convergence by using the weighted modulus of continuity and afterwards, we present a nontrivial application.     

Structure of 4,4′-butane-(1,4,7-three-p-tolylsulphonyl-1,4,7-three amine) diphthalonitrile

Abstract

The crystal structure of the title compound, C₄₁ H₃₅ N₇ O₆ S₃ was determined as monoclinic by single crystal X-Ray diffraction technique. The molecular structure was identified by IR, ¹H-NMR, ¹³C-NMR and elemental analysis. The crystal parameters of this compound are as follows: monoclinic P 2 1/n, a = 12.694(2) Å, b = 26.204(2) Å, c = 13.005(2) Å, β = 102.95(2)°, V = 4216.02(1) Å.³, Z = 4, Dx = 1.289 g/cm³, F(000) = 1704, λ (MoKα) = 0.71070 Å, μ = 0.2 mm^?1. The structure was solved by SHELXS-97 and refined by SHELXL-97. R = 0.06 for 3178 observed reflections with I > 2σ (I).     

Electrochemical adsorption properties and inhibition of copper corrosion in chloride solutions by ascorbic acid: experimental and theoretical investigation

In this study, the effect of ascorbic acid in the electrochemical behavior of copper has been investigated in 3.5 % NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy. Current-potential curve and Nyquist diagrams were obtained in different concentrations of ascorbic acid. The surface morphology of copper after its exposure to 3.5 % NaCl solution with and without of ascorbic acid was examined by scanning electron microscopy. The obtained results show that ascorbic acid inhibits corrosion of copper in 3.5 % NaCl solution. The inhibition activity of ascorbic acid increases with a decrease in the concentration of ascorbic acid.