Chemistry / Kimya

Permanent URI for this collectionhttps://hdl.handle.net/11147/4072

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  • Article
    Citation - WoS: 16
    Citation - Scopus: 19
    Nmr Studies on Natural and Synthetic Amavadin
    (Elsevier Ltd., 2000) Armstrong, Elaine M.; Collison, David; Ertok, Nigar; Garner, Catherine D.
    The stereochemistry of isolated natural product Amavadin, which contains a 1:2 complex of V(IV) with N-hydroxyimino-2,2′-dipropionic acid (HIDPAH3), and some synthetic complexes have been investigated. Amavadin was isolated from Amanita muscaria and oxidized with [NH4]2[Ce(NO3)6]. H2[Δ-V(S,S-HIDPA)2].3H2O, H2[Δ,Λ-V(S,S-HIDPA)2].3H2O and their equivalent oxidized species have been synthesized and characterized spectroscopically. A combination of COSY, NOE, 1H, 13C-NMR and CD spectroscopy have been used to prove that the isolated natural product Amavadin consists of an almost equal mixture of the Δ- and Λ-isomers of [V(S,S-HIDPA)2]2-. The stereochemistry of isolated natural product Amavadin, which contains a 1:2 complex of V(IV) with N-hydroxyimino-2,2'-dipropionic acid (HIDPAH3), and some synthetic complexes have been investigated. Amavadin was isolated from Amanita muscaria and oxidized with [NH4]2[Ce(NO3)6]. H2[Δ-V(S,S-HIDPA)2].3H2O, H2[Δ,Λ-V(S,S-HIDPA)2].3H2O and their equivalent oxidized species have been synthesized and characterized spectroscopically. A combination of COSY, NOE, 1H, 13C-NMR and CD spectroscopy have been used to prove that the isolated natural product Amavadin consists of an almost equal mixture of the Δ- and Λ-isomers of [V(S,S-HIDPA)2]2-.
  • Article
    Citation - WoS: 31
    Citation - Scopus: 34
    6-Bicycloaryl Substituted (s)- and (r)-5,6 Asymmetric Synthesis, and Anti-Proliferative Properties
    (Elsevier Ltd., 2009) Kasaplar, Pınar; Yılmazer, Özgür; Çağır, Ali
    (R)-Goniothalamin, is a member of styryl lactones, possesses selective cytotoxicity against cancer cell lines. In this work, replacement of styryl substituent with 2-naphthyl and 3-quinoyl gave new analogues which may have less conformational changes compared to the lead compound. Anti-proliferative tests indicated that 2-naphthyl substituted (R)-5,6-dihydro-2H-pyran-2-one has slightly better cytotoxicity than (R)-goniothalamin. To clarify the effect of 2-naphthyl substituent additional aryl substituted (R)-5,6-dihydro-2H-pyran-2-ones have been synthesized enantioselectively and tested against PC-3 and MCF-7 cell lines.
  • Article
    Citation - WoS: 61
    Citation - Scopus: 69
    Assessment of the Molecular Weight Distribution of Tannin Fractions Through Maldi-Tof Ms Analysis of Protein-Tannin Complexes
    (American Chemical Society, 2007) Mané, C.; Sommerer, N.; Yalçın, Talat; Cheynier, V.; Cole, R. B.; Fulcrand, H.
    An innovative mass spectrometry method was developed for determining mass distributions of tannin fractions that cannot be approached through direct MALDI-TOF analysis. It was applied to three procyanidin fractions with average degrees of polymerizations = 3, 9, and 28, respectively, and one gallotannin fraction (Tara tannin). The proposed approach consists of MALDI-TOF analysis of the soluble complexes formed between these tannin fractions and bovine serum albumin (BSA). Complexes were detected as an unresolved "hump" following the BSA signal, and spectra were mathematically processed to determine the parameters relative to the protein-tannin complexes, which are the number-average molecular weight (Mn), the weight-average molecular weight (Mw), and the polydispersity index (PI) for each tannin fraction. Regarding condensed tannins, results are consistent with those of the standard method (thiolysis followed by HPLC separation) for all tested fractions. The method was successfully applied to a hydrolyzable tannin fraction but no standard method is available for comparison.
  • Article
    Citation - WoS: 33
    Citation - Scopus: 33
    Modification of a Montmorillonite-Illite Clay Using Alkaline Hydrothermal Treatment and Its Application for the Removal of Aqueous Cs+ Ions
    (Elsevier Ltd., 2006) Öztop, Bahar; Shahwan, Talal
    A montmorillonite-illite clay was modified using alkaline hydrothermal treatment (reflux method) and applied to the removal of aqueous Cs+ ions. The alkaline solutions were prepared by dissolving NaOH in seawater and in distilled water, and the effect of the two alkaline media on the sorption capacities of the modified clay was discussed. The modified materials were characterized using XRD, SEM/EDS, and FTIR. As a result of the modification, the original mineral was partially transformed into a zeolitic material with spherical morphology. The results showed that the modification improved the Cs+ uptake capacity of the starting clay, with the clay modified in distilled water medium demonstrating higher sorption capacity. The sorption data were adequately described using the Freundlich and Dubinin-Radushkevich isotherm models.
  • Article
    Citation - WoS: 25
    Citation - Scopus: 20
    Rhodium-Catalyzed Carbonylative Arylation of Alkynes With Arylboronic Acids: an Efficient and Straightforward Method in the Synthesis of 5-Aryl
    (Royal Society of Chemistry, 2006) Aksın, Özge; Dege, Nurcan; Artok, Levent; Türkmen, Hayati; Çetinkaya, Bekir
    5-Aryl-2(5H)-furanones can be synthesized by the Rh-catalyzed reactions of arylboronic acids with internal alkynes under a CO atmosphere.
  • Letter
    Citation - WoS: 46
    Citation - Scopus: 53
    A Characterization Study of Some Aspects of the Adsorption of Aqueous Co2+ Ions on a Natural Bentonite Clay
    (Elsevier Ltd., 2006) Shahwan, Talal; Erten, Hasan N.; Ünügür, S.
    The natural bentonite used in this study contained montmorillonite in addition to low cristobalite. The uptake of aqueous Co2+ ions was investigated as a function of time, concentration, and temperature. In addition, the change in the interlayer space of montmorillonite was analyzed using XRPD, and the distribution of fixed Co2+ ions on the heterogeneous clay surface was recorded using EDS mapping. The sorbed amount of Co2+ appeared to closely follow Freundlich isotherm, with the sorption process showing apparent endothermic behavior. The relevance of the apparent Δ Ho values is briefly discussed. Analysis of the Co-sorbed bentonite samples using SEM/EDS showed that the montmorillonite fraction in the mineral was more effective in Co2+ fixation than the cristobalite fraction. XRPD analysis demonstrated that the interlayer space of montmorillonite was slightly modified at the end of sorption.
  • Article
    Citation - WoS: 57
    Citation - Scopus: 62
    Effect of Various Treatment and Glazing (coating) Techniques on the Roughness and Wettability of Ceramic Dental Restorative Surfaces
    (Elsevier Ltd., 2006) Aksoy, Gökhan; Polat, Hürriyet; Polat, Mehmet; Çoşkun, G.
    Surface treatment procedures such as grinding and polishing are needed to provide the ceramic dental restorative materials with proper fitting and occlusion. The treated surfaces are customarily glazed to improve the strength and smoothness. Though smoothness and wetting of the dental surfaces are important to minimize bacterial plaque retention, influence of the surface treatment and glazing procedures on the final surface roughness and its correlation to wettability are overlooked. In this work, effect of various treatment (diamond fraising, stoning, sanding and aluminum oxide and rubber polishing) and glazing (auto and overglazing) techniques on the final roughness and the resulting wettability of dental ceramic surfaces were investigated using scanning electron microscopy (SEM) observations and atomic force microscopy (AFM) scans, 75 scans per sample. The surfaces were characterized and assigned an average roughness measure, Ra. The wettability of the same surfaces was evaluated using micro-contact angle measurements (25 micro-bubbles placed on a grid on each surface) to correlate the final surface roughness and wettability. The results show that overglazing prevails over surface irregularities from different treatment procedures and provides homegeneously smooth surfaces with mean Ra < 10 nm. It also produces uniformly wetted surfaces with low contact angles around 20°. The autoglazed surfaces are less smooth (mean Ra around 50 nm) and displays sporadic topographic irregularities. They display larger and less uniform contact angles ranging between 35° and 50°. The results suggest that overglazing should be preferred after surface treatment to obtain a smooth and well-wetted dental ceramic surface.
  • Article
    Citation - WoS: 259
    Citation - Scopus: 284
    Heavy Metal Removal From Waste Waters by Ion Flotation
    (Elsevier Ltd., 2007) Polat, Hürriyet; Erdoğan, D.
    Flotation studies were carried out to investigate the removal of heavy metals such as copper (II), zinc (II), chromium (III) and silver (I) from waste waters. Various parameters such as pH, collector and frother concentrations and airflow rate were tested to determine the optimum flotation conditions. Sodium dodecyl sulfate and hexadecyltrimethyl ammonium bromide were used as collectors. Ethanol and methyl isobutyl carbinol (MIBC) were used as frothers. Metal removal reached about 74% under optimum conditions at low pH. At basic pH it became as high as 90%, probably due to the contribution from the flotation of metal precipitates.
  • Article
    Citation - WoS: 211
    Citation - Scopus: 246
    A Radiotracer Study of the Adsorption Behavior of Aqueous Ba2+ Ions on Nanoparticles of Zero-Valent Iron
    (Elsevier Ltd., 2007) Çelebi, O.; Üzüm, Çağrı; Shahwan, Talal.; Erten, Hasan N
    Recently, iron nanoparticles are increasingly being tested as adsorbents for various types of organic and inorganic pollutants. In this study, nanoparticles of zero-valent iron (NZVI) synthesized under atmospheric conditions were employed for the removal of Ba2+ ions in a concentration range 10-3 to 10-6 M. Throughout the study, 133Ba was used as a tracer to study the effects of time, concentration, and temperature. The obtained data was analyzed using various kinetic models and adsorption isotherms. Pseudo-second-order kinetics and Dubinin-Radushkevich isotherm model provided the best correlation with the obtained data. Observed thermodynamic parameters showed that the process is exothermic and hence enthalpy-driven.
  • Article
    Citation - WoS: 28
    Citation - Scopus: 28
    Speciation and Preconcentration of Inorganic Antimony in Waters by Duolite Gt-73 Microcolumn and Determination by Segmented Flow Injection-Hydride Generation Atomic Absorption Spectrometry (sfi-Hgaas)
    (Elsevier Ltd., 2005) Erdem, Aslı; Eroğlu, Ahmet Emin
    A selective matrix removal/separation/enrichment method, utilizing a microcolumn of a chelating resin with SH functional groups (Duolite GT-73), was proposed for the determination of Sb(III) in waters by segmented flow injection-hydride generation atomic absorption spectrometry (SFI-HGAAS). The resin was selective to Sb(III) at almost all pH and acidity values employed, whereas Sb(V) was not retained at all and could be determined after a pre-reduction step with l-cysteine. Spike recoveries were tested at various concentration levels in different water types and were found to vary between 85 and 118%. Accuracy of the proposed methodology was checked by analyzing a standard reference material and a good correlation was found between the determined (13.3 ± 1.1 μg l-1) and the certified value (13.79 ± 0.42 μg l-1). The method was applied to several bottled drinking water samples for antimony determination with and without preconcentration and none of the samples were found to contain antimony above the permissible level (5 μg l-1). The characteristic concentration (the concentration of the analyte corresponding to an absorbance of 0.0044) was 0.55 μg l-1 and the 3 s limit of detection (LOD) based on five times preconcentration was 0.06 μg l-1. The applicability of the microcolumn separation/preconcentration/matrix removal method for flow injection systems was also demonstrated.