Chemistry / Kimya
Permanent URI for this collectionhttps://hdl.handle.net/11147/4072
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Article Citation - WoS: 2Reduction of Carbon Dioxide During the Synthesis of Metal Nano-Particles in Water(Elsevier Ltd., 2003) Polat, Hürriyet; Cohen, H; Meyerstein, D; Rusonik, I.An effort was made to synthesize "carbon-free" metal (Fe-0, Co-0, Ni-0) nano-particles via the reduction of their salts with BH4- in aqueous solutions. Surprisingly it was found that when the synthesis is carried out in the presence of CO2, e.g., in aerated solutions, the CO2 is catalytically reduced by BH(4)(-)on the surface of the metal particles. Carbon-free metals can be prepared by reduction under an inert atmosphere. Thus metal surfaces might have acted as catalysts for CO2 fixation, probably via the initial formation of carbon clusters, in the reductive atmosphere in the prebiotic era. (C) 2003 Elsevier B.V. All rights reserved.Article Citation - WoS: 16Citation - Scopus: 19Nmr 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: 31Citation - Scopus: 346-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: 41Citation - Scopus: 42Characterization of Materials Used in the Execution of Historic Oil Paintings by Xrd, Sem-Eds, Tga and Libs Analysis(Elsevier Ltd., 2009) Şerifaki, Kerem; Böke, Hasan; Yalçın, Şerife; İpekoğlu, BaşakIn this study, material characteristics of historic oil paintings in a 19th century church in Ayvali{dotless}k/Turkey were investigated to propose the treatments to be used in their conservation and protection. For this purpose, physical, chemical and mineralogical compositions and the microstructure of the paintings were determined by X-ray Diffraction, Scanning Electron Microscope, Thermo Gravimetric Analyzer, Differential Scanning Calorimeter, Infrared Spectroscopy and Laser Induced Breakdown Spectroscopy. Analysis results showed that the paintings were composed of very thin binding and white priming layers on which the pigments were applied. Binding layers were composed of polymerized vegetable oil with Zinc Oxide. Priming layers were composed of anglesite mineral in polymerized vegetable oil. Pigments used in paintings were mainly green earth, red chrome and iron oxide.Article Citation - WoS: 4Citation - Scopus: 6The Effect of Additives on Hydrodesulfurization of Dibenzothiophene Over Bulk Molybdenum Sulfide: Increased Catalytic Activity in the Presence of Phenol(Elsevier Ltd., 2008) Gül, Ömer; Atanur, Osman M.; Artok, Levent; Erbatur, OktayThe effect of various additive organic reagents on the activation of MoS3 as molybdenum sulfide catalyst precursor during hydrodesulfurization reaction of dibenzothiophene was studied. It was found that the presence of phenol or 1-naphthol greatly promoted the activity of the catalyst, while tetralin, 9,10-dihydrophenanthrene, ethylbenzene, and pyridine reagents were found to be detrimental for the activity of the catalyst.Article Citation - WoS: 2Citation - Scopus: 2Polarized Absorption Spectra of Highly Oriented Two-Dimensional Aggregates of Tetrachlorobenzimidazolocarbocyanine in Thin Films(Elsevier Ltd., 2008) Özçelik, Serdar; Gülen, DemetReaching a control on the mesoscopic morphology and internal molecular arrangement of cyanine aggregates is an important step for realization of devices with tailor-made optical properties. Despite a wealth of research, understanding of the relationship between molecular organization, excitonic states and dynamics of aggregates is still preliminary. To this end, we have employed polarized absorption spectroscopy to investigate the relationship between internal molecular organization and excitonic states of J-aggregates in 1,1′,3,3′tetraethyl-5,5′,6,6′-tetrachlorobenzimidazolocarbocyanine (TTBC) thin films in poly-vinyl alcohol (PVA). Angular dependence of the UV-vis spectra has been measured at 11 different orientations between the electric field polarization and the macroscopic alignment axis. Aggregate spectral response consisted of an asymmetrically split Davydov pair of bands exhibiting opposite polarization: an H-band (505 nm, Lorentzian-like, polarized along the macroscopic film axis) and a J-band (594 nm, one-dimensional J-aggregate like band shape, polarized perpendicular to the macroscopic film axis). The polarized absorption observations were found to be consistent with a herringbone model for which the internal molecular arrangement, the excited state structure and dynamics have recently been detailed by us upon interpretation of isotropic absorption data in ionic aqueous solution.Article Citation - WoS: 4Citation - Scopus: 6Absorption Spectrum of Monomeric Pseudoisocyanine: a New Perspective and Its Implications for Formation and Spectral Response of J-Aggregates in Solution and in Thin Films(Elsevier Ltd., 2008) Gülen, Demet; Özçelik, SerdarWe argued against the current spectral assignment for absorption spectrum of monomeric PIC which is widely accepted since the pioneering works of Scheibe and Jelley [G. Scheibe, Angew. Chem. 49 (1936) 563; E.E. Jelly, Nature 138 (1936) 1009]. A new spectrum is presented along with its conceptual basis. The hypothesized spectrum attributes the previous 0-0 (≈525 nm) and 0-1 (≈490 nm) assignments, respectively, to intermediates acting as the precursor of J-aggregates and to the 0-0 transition of monomeric PIC and brings the spectrum in accord with the seemingly universal spectral fingerprint of cyanines. The hypothesis is used to analyze and interpret the temperature dependence of the UV-vis absorption of PIC aggregates in saline aqueous solution by incorporating the J-band simulations within frenkel exciton formalism. Its implications for aggregate formation kinetics are given on the basis of current spectroscopic evidence. The hypothesis readily answers several long-standing questions: Why compared to many other cyanines at least an order of magnitude higher dye concentration is needed to form J-aggregates of PIC? Why are there no precursors, since aggregation is expected to be a consecutive process? A large number of observations on steady-state and time-resolved spectral properties, and aggregation kinetics in solution/thin films are likely to find reasonable explanations within this hypothesis.Article Citation - WoS: 12Citation - Scopus: 12Modification of Metal/Semiconductor Junctions by Self-Assembled Monolayer Organic Films(Elsevier Ltd., 2009) Yakuphanoğlu, Fahrettin; Okur, Salih; Özgener, HüseyinTwo new metal/molecule/semiconductor contacts, Au/n-Si/TDA/Au and Au/p-Si/ODM/Au, were fabricated to understand effect of organic compounds, tridecylamine and octadecylmercaptan self-assembled monolayer (SAM) films, on electrical charge transport properties of the metal/semiconductor junctions. The morphology of the organic monolayers deposited on Si substrates was investigated by atomic force microscopy. The molecular coverage of ODM deposited on p-Si is poorer than that of TDA on n-Si substrate. The ideality factors of the p-Si/ODM and n-Si/TDA diodes were found to be 1.66 and 1.48, respectively. The electrical results show that the tridecylamine monolayer passivated junction has a lower ideality factor. The ideality factor indicates clear dependence on two different type functional groups R-SH (Thiol) and R-NH2 (Amin) groups and it increases with different functional groups of organic molecule. The barrier height φb value of the n-Si/TDA diode is smaller than that of p-Si/ODM diode, as a result of chain length of the SAM organic molecules. The interface state density Dit values of the diodes were determined using conductance technique. The n-Si/TDA diode has the smaller interface state density according to p-Si/ODM diode. We have evaluated that the organic molecules control the electronic parameters of metal/semiconductor diodes and thus, organic modification helps to get one step closer towards to new organic assisted silicon based microelectronic devices.Article Citation - WoS: 10Citation - Scopus: 10Determination of the Particle Interactions, Rheology and the Surface Roughness Relationship for Dental Restorative Ceramics(Elsevier Ltd., 2009) Kes, Mürşide; Polat, Hürriyet; Keleşoğlu, Serkan; Polat, Mehmet; Aksoy, GökhanThe effect of inter-particle interactions on the slurry properties and the final surface roughness of the dental ceramic restoratives was investigated. A commercial dental ceramic powder, IPS Empress 2 veneer, was used as the raw material. The magnitudes of the particle-particle interactions were computed by the DLVO theory for the ceramic slurries of different electrolyte solutions (0.1 M, 0.25 M, 0.5 M, 0.75 M, 1 M NaCl and CaCl2). As expected, the energies of particle-particle interactions were influenced significantly by the presence of electrolytes. These computations demonstrated that addition of electrolytes leads to a progressive depression of the repulsive double layer forces. The absence of these forces should inevitably lead to agglomeration caused by the ever-present van der Waals forces. The rheological measurements carried out using the slurries with same solution properties supported the findings of the DLVO computations. It was found that dental ceramic slurries showed a Newtonian behavior in the absence of electrolytes, which is indicative of little or no agglomeration in the slurry. On the other hand, the same slurries displayed a non-Newtonian, shear thinning behavior in the presence of electrolytes which can be attributed to agglomeration or gelation. Roughness of the ceramic surfaces produced from these slurries was studied by SEM analysis and profilometer measurements. Contact angle studies were also carried out on the same surfaces. It was observed that the surface became rougher initially with electrolyte addition to a maximum, most probably due to formation of isolated agglomerates due to a reduction of the repulsive double layer forces. After reaching a maximum, surface roughness decreased to a much lower value with further increase in electrolyte concentration. This was most probably caused by the formation of a relatively homogeneous, gel-like structure within the extensively agglomerated slurry due to a complete collapse of the double layer.Article Citation - WoS: 27Citation - Scopus: 30Rhodium Catalyzed Reaction of Internal Alkynes With Organoborons Under Co Atmosphere: a Product Tunable Reaction(Elsevier Ltd., 2009) Artok, Levent; Kuş, Melih; Aksın, Özge; Dege, Fatma Nurcan; Özkılınç, Fatma YeldaAlkynes react with organoborons under a CO atmosphere in the presence of a rhodium(I) catalyst to afford mainly 5-aryl-2(5H)-furanones, α,β-unsaturated ketones, and indanones. The product selectivity can be tuned by modifying the reaction conditions.