Chemistry / Kimya
Permanent URI for this collectionhttps://hdl.handle.net/11147/4072
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Article Citation - WoS: 21Citation - Scopus: 21Palladium-Catalyzed Alkoxycarbonylation of Conjugated Enyne Oxiranes: a Diastereoselective Method for the Synthesis of 7-Hydroxy(American Chemical Society, 2015) Kuş, Melih; Artok, Levent; Aygün, MuhittinPalladium-catalyzed alkoxycarbonylative 1,5-substitution of conjugated enyne oxiranes provides a diastereoselective route to (E)-configured 7-hydroxy-2,3,5-trienoates. The reactions proceeded in a highly stereoselective manner, possibly through sequential formation of π-allylpalladium and σ-vinylallenyl palladium complexes. The major diastereomeric form of the product is determined by the configuration of the alkenyl moiety of the substrate.Article Citation - WoS: 56Citation - Scopus: 57Dynamic Nuclear Polarization of Spherical Nanoparticles(Royal Society of Chemistry, 2013) Akbey, Ümit; Altın, Burcu; Linden, Arne; Özçelik, Serdar; Gradzielski, Michael; Oschkinat, HartmutSpherical silica nanoparticles of various particle sizes (∼10 to 100 nm), produced by a modified Stoeber method employing amino acids as catalysts, are investigated using Dynamic Nuclear Polarization (DNP) enhanced Nuclear Magnetic Resonance (NMR) spectroscopy. This study includes ultra-sensitive detection of surface-bound amino acids and their supramolecular organization in trace amounts, exploiting the increase in NMR sensitivity of up to three orders of magnitude via DNP. Moreover, the nature of the silicon nuclei on the surface and the bulk silicon nuclei in the core (sub-surface) is characterized at atomic resolution. Thereby, we obtain unique insights into the surface chemistry of these nanoparticles, which might result in improving their rational design as required for promising applications, e.g. as catalysts or imaging contrast agents. The non-covalent binding of amino acids to surfaces was determined which shows that the amino acids not just function as catalysts but become incorporated into the nanoparticles during the formation process. As a result only three distinct Q-types of silica signals were observed from surface and core regions. We observed dramatic changes of DNP enhancements as a function of particle size, and very small particles (which suit in vivo applications better) were hyperpolarized with the best efficiency. Nearly one order of magnitude larger DNP enhancement was observed for nanoparticles with 13 nm size compared to particles with 100 nm size. We determined an approximate DNP penetration-depth (∼4.2 or ∼5.7 nm) for the polarization transfer from electrons to the nuclei of the spherical nanoparticles. Faster DNP polarization buildup was observed for larger nanoparticles. Efficient hyperpolarization of such nanoparticles, as achieved in this work, can be utilized in applications such as magnetic resonance imaging (MRI).Article Citation - WoS: 30Citation - Scopus: 30Glycidyl-Methacry Late-Based Electrospun Mats and Catalytic Silver Nanoparticles(John Wiley and Sons Inc., 2008) Demir, Mustafa Muammer; Uğur, Gökçe; Gülgün, Mehmet A.; Menceloğlu, Yusuf Z.P(AN-GMA) and PGMA fibers coated with monodisperse silver nanoparticles have been prepared by a combination of electrospinning and electroless plating. The morphology of the electrospun fibers remains unchanged after surface hydrazination. Oxidation of hydrazine in an ammoniacal solution of AgNO 3 reduces and deposits silver atoms along the fiber surface, which then coalesce to Ag particles. The size of the silver nanoparticles is varied between 20-60 nm. Since the density of the active sites for silver reduction is lower in P(AN-GMA), a smaller particle size could be obtained. The catalytic activity of the silver nanoparticles has been confirmed.Article Citation - WoS: 83Precipitation of Monodisperse Zno Nanocrystals Via Acid-Catalyzed Esterification of Zinc Acetate(Royal Society of Chemistry, 2006) Demir, Mustafa Muammer; Muñozz-Espí, Rafael; Lieberwirth, Ingo; Wegner, GerhardA wet-chemical method to produce zinc oxide nanocrystals of monodisperse size distribution (diameter range of 20-80 nm) is presented. The synthesis starts from zinc acetate dihydrate which is converted to ZnO in the presence of 1-pentanol in m-xylene at 130 °C. We report for the first time catalysis of this reaction by p-toluene sulfonic acid monohydrate (p-TSA), which allows a shorter reaction time and improves both the reproducibility of the particle size distribution and the crystallinity of the particles. The reaction can be scaled up to give multigram quantities of product per batch. Particles were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and photoluminesence (PL) spectroscopy. Room temperature PL spectra of ZnO prepared without catalyst exhibit a strong and sharp UV emission band at ca. 385 nm and a weak and very broad green-yellow visible emission centered at ca. 550-560 nm. However, for nanoparticles precipitated in the presence of p-TSA, the UV emission is enhanced by a factor of 4, which can be correlated with the improvement of crystal perfection. A particle formation mechanism is discussed.Article Citation - WoS: 64Citation - Scopus: 67Hierarchically Structured Metal Oxide/Silica Nanofibers by Colloid Electrospinning(American Chemical Society, 2012) Horzum Polat, Nesrin; Mun˜oz-Espí, Rafael; Glasser, Gunnar; Demir, Mustafa Muammer; Landfester, Katharina; Crespy, DanielWe present herein a new concept for the preparation of nanofibrous metal oxides based on the simultaneous electrospinning of metal oxide precursors and silica nanoparticles. Precursor fibers are prepared by electrospinning silica nanoparticles (20 nm in diameter) dispersed in an aqueous solution of poly(acrylic acid) and metal salts. Upon calcination in air, the poly(acrylic acid) matrix is removed, the silica nanoparticles are cemented, and nanocrystalline metal oxide particles of 4-14 nm are nucleated at the surface of the silica nanoparticles. The obtained continuous silica fibers act as a structural framework for metal oxide nanoparticles and show improved mechanical integrity compared to the neat metal oxide fibers. The hierarchically nanostructured materials are promising for catalysis applications, as demonstrated by the successful degradation of a model dye in the presence of the fibers.Conference Object Citation - WoS: 7Citation - Scopus: 8Acylation of 2-Methoxynaphthalene Over Ion-Exchanged Ss-Zeolite(Elsevier Ltd., 2002) Kantarlı, İsmail Cem; Artok, Levent; Bulut, Hatice; Yılmaz, Selahattin; Ülkü, SemraFriedel-Crafts acylation of 2-Methoxynaphthalene was carried out over various ion-exchanged β zeolites (Mn+β, where Mn+: In3+, Zn2+, Al3+, Fe3+, La3+) with various anhydride (acetic, propionic and benzoic anhydrides), or acyl chloride (acetyl, propionyl and benzoyl chlorides) acylating reagents. The results suggested that selectivity towards the 6-substituted products was higher with the larger size anhydrides, propionic and benzoic anhydrides. The metal cation type within the zeolite significantly influenced the extent of conversion and product distribution. That La3+ exchanged zeolite displayed higher selectivity for the 6-position acylated product with anhydrides ascribed mainly to narrowing of channels by the presence of La(OH)2+ ions that leave no room for the formation of more bulky isomeric forms and to enhanced Bronsted acidity of the zeolite. With acyl chlorides, the recovery of ketone products was found to be remarkably low. 1-Acyl-2-methoxynaphthalenes actively underwent deacylation when acyl chlorides were used as the acylation reagent.