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Publication Metadata only 3D printed poly(lactic acid) scaffolds modified with chitosan and hydroxyapatite for bone repair applications(Elsevier, 2020) N/A; N/A; N/A; N/A; Department of Chemistry; Department of Chemical and Biological Engineering; Department of Chemistry; Nazeer, Muhammad Anwaar; Önder, Özgün Can; Sevgili, İlkem; Yılgör, Emel; Kavaklı, İbrahim Halil; Yılgör, İskender; PhD Student; PhD Student; PhD Student; Researcher; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; College of Sciences; N/A; N/A; N/A; N/A; 40319; 241813D printed poly(lactic acid) (PLA) scaffolds surface modified with chitosan (CS) and hydroxyapatite (HA) to produce a novel bioactive composite scaffold is reported. Excellent mechanical properties of PLA, the bioactivity of CS, and osteogenic characteristics of HA are combined to fabricate composite scaffolds using a simple desktop 3D printer. Scaffolds were characterized through attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD) and water contact angle measurements before and after modification. Formic acid was used as a solvent to prepare stable CS/HA dispersions and was found to be a suitable solvent for producing PLA/CS/HA composites. Surface properties of modified scaffolds were superior in terms of hydrophilicity and bioactivity, which resulted in enhanced attachment and proliferation of human osteosarcoma cells in vitro compared to the unmodified PLA scaffolds.Publication Metadata only A comparative study on the effect of monodisperse Au and Ag nanoparticles on the performance of organic photovoltaic devices(Elsevier, 2021) Kacus, Hatice; Sevim, Melike; Biber, Mehmet; Baltakesmez, Ali; Aydogan, Sakir; Department of Chemistry; Metin, Önder; Faculty Member; Department of Chemistry; College of Sciences; 46962The monodisperse Au (similar to 5 nm) and Ag (similar to 3 nm) nanoparticles used in this study were obtained using surfactant-assistant solvothermal methods and characterized by XRD TEM and SEM. Then, these nanoparticles were embedded into the P3HT:PCBM photoactive layer at different ratios and the effects of the nanoparticles on the performance of the organic solar cells have been studied by varying the loading percent of the NPs in the range of 0.5-2 wt%. The best solar cell composition was determined to be 1 wt% for Au NPs and 0.5 wt% for Ag NPs. Optical absorption spectrum of P3HT:PCBM, P3HT:PCBM:AuNPs and P3HT:PCBM:AgNPs active layers were obtained using UV-visible spectroscopy. The J-V plots of ITO/PEDOT:PSS/P3HT:PCBM/LiF/Al solar cells having 1.10(-6) m(2) OSC area and with different Au NPs and Ag NPs loading ratios in the P3HT:PCBM were obtained under air mass (AM) 1.5G illumination. Open circuit voltage, short-circuit current density, fill factor, and power conversion efficiency of the OSC were calculated. The highest PCE values were obtained as 3.35% for Au NPs and as 3.50% for Ag NPs doped devices. This increase in PCEs was explained by a plasmonic effect that stems from the metallic NPs.Publication Metadata only A novel anthracene functionalized dibenzoxanthene fluorophore for copper (II) sensing(Elsevier, 2021) Özükanar, Özge; Ünlü, Caner; Kumbaracı, Volkan; Department of Chemistry; Gündüz, Hande; Researcher; Department of Chemistry; College of Sciences; 224496Dibenzoxanthene derivatives are widely used in metal ion sensing applications. Especially, fluorescent dibenzoxanthene derivatives are potential candidate to sense metal ions in various solvent systems. However, most of the studies are focused on either metal sensing in aqueous solutions, or sensing of the extremely toxic metal ions, such as Pb2+ and Hg2+. In this study, a novel benzyl functionalized dibenzoxanthene derivative and a novel fluorescent anthracene functionalized dibenzoxanthene derivative were synthesized to sense metal ions in polar aprotic solvent systems by using UV-Vis spectroscopy and Fluorescence spectroscopy. As benzyldibenzoxanthene was sensitive to multiple metal ions (Pb2+, CO2+, and Cu2+), novel anthracenyldibenzoxanthene was only sensitive to Cu2+ with the binding capacity of one anthracenyl-dibenzoxanthene to three Cu2+ ions, thus the copper sensitivity was increased. The binding affinity of dibenzoxanthene derivatives with Cu2+ has been analyzed by H-1 NMR and High-resolution XPS.Publication Metadata only A novel europium (iii) nitridoborate eu-3[b3n6]: synthesis, crystal structure, magnetic properties, and Raman spectra(Elsevier, 2016) Prots, Yurii; Foerster, Tobias; Sichelschmidt, Joerg; Schappacher, Falko M.; Poettgen, Rainer; Ormeci, Alim; Department of Chemistry; N/A; Department of Chemistry; Aydemir, Umut; Kokal, İlkin; Somer, Mehmet Suat; Faculty Member; Researcher; Faculty Member; Department of Chemistry; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; 58403; N/A; 178882A novel europium (III) nitridoborate, Eu-3[B3N6], was successfully synthesized by oxidation of Eu-3(II)[BN2](2) with Br-2 at 1073 K. The compound crystallizes in the trigonal space group R (3) over barc (No:167) with a=11.9370(4) angstrom, c=6.8073(4) angstrom, and Z=6. The crystal structure of Eu-3[B3N6] consists of isolated, planar cyclic [B3N6](9-) units which are charge-balanced by Eu3+ cations. The oxidation state of Eu was investigated by Mossbauer spectroscopy, electron spin resonance (ESR) spectroscopy, and quantum chemical calculations. The Eu-151 Mossbauer spectroscopic measurement at 77 K reveals that the main signal at delta=0.93(7) mm/s is originating from trivalent Europium. Eu-3[B3N6] showed no ESR signal in accordance with a non-magnetic (J=0) F-7(0) ground state of the 4f(6) configuration. Quantum chemical calculations find six electrons in the 4f subshell (4f(6)) of Eu indicating an oxidation state of +3. We present for the first time the vibrational spectra of a compound with cyclic trimer [B3N6](9-) moieties. The Raman spectrum of Eu-3[B3N6] is in good agreement with the predicted number of modes for the spectroscopically relevant cyclic [B3N6](9-) group with D-3h symmetry.Publication Metadata only A post-HF study on the halogen bonding interaction of pyrene with diatomic halogen molecules(Wiley, 2016) Sütay, Berkay; Yurtsever, Mine; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129We present a detailed SCS-MP2 study on the potential energy curves (PEC) for interactions between diatomic halogen molecules and pyrene. BSSE corrected CCSD[T] energies at equilibrium distances are computed and compared to CCSD(T) energies. The most stable conformation of these weakly bound van der Waals complexes is almost linear in the perpendicular direction to the pyrene plane. The complexes of highly polarizable bromine and iodine molecules with pyrene are very stable and they carry rather large number of vibrational states. Despite its small size, F-2 also forms strong halogen bonding similar to Br-2 and I-2. The interaction between Cl-2 and pyrene is the weakest and it is attributed to the highest polarizability/molar mass ratio of chlorine among the others. I-2-pyrene is found to be the most stable complex due to the strongest mutual polarization effects and is carrying more than 60 vibrational states. Due to the rather large number of electrons in some complexes, the relativistic corrections are also considered.Publication Metadata only A quantum mechanical study of the electrochemical polymerization of pyrrole(Elsevier Science Sa, 2001) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Mechanism for the electrochemical polymerization of pyrrole is studied using accurate density functional theory; (DFT) calculations. The primary emphasis is on the structures and stability of intermediates generated during various mechanisms. Structures of the radical cations, which play role in reactions, an optimized to elucidate radical-radical and radical-neutral pathways. The competing probabilities of reactions between various size oligomers are discussed in terms of their thermodynamical stability.Publication Metadata only A theoretical study of structural defects in conjugated polymers(Elsevier Science Sa, 1999) Yurtsever, Mine; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Accurate ab-initio calculations are performed for pyrrole and thiophene oligomers bonded through alpha and beta carbons. The thermodynamical stabilitiy of all possible binding types including the branched forms of tetramers and pentamers are compared. Employing the probabilities obtained from these calculations, a Monte Carlo type growth scheme is applied to predict branching as functions of the chain length and temperature. A high degree of branching for polypyrrole is reported whereas the linear chains dominate the structure of polythiophene.Publication Metadata only A universal method for the preparation of magnetic and luminescent hybrid nanoparticles(American Chemical Society (ACS), 2010) Topal, Uğur; N/A; N/A; Department of Chemistry; Kaş, Recep; Sevinç, Esra; Acar, Havva Funda Yağcı; Master Student; Master Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 178902Hybrid nanoparticles (MDOTs) composed of luminescent quantum dots (QDs) and superparamagnetic iron oxides (SPIOs) were prepared by the ligand-exchange mechanism in a simple and versatile extraction method. In this method, aqueous QDs (CdS or CdTe) coated with carboxylated ligands exchange the fatty acid (lauric acid) coating of SPIOs in a water chloroform extraction process. QDs form a coating around SPIOs and transfer them into the aqueous phase in high efficiency. The method worked successfully with both small and polymeric coating molecules selected as cysteine, 2-mercaptopropionic acid, and a poly(acrylic acid)/mercaptoacetic acid mixture. The original properties of the nanoparticles were well-preserved in the hybrid structures: All MDOTS showed ferrofluidic behavior and had a luminescence in the original color of the QD. Magnetic properties and the luminesence intensity of MDOTs can be easily tuned with the SPIO/QD ratio. All particles are small and show very good stability (optical and colloidal) over months. For stable MDOTs with good luminescence properties, highly luminescent aqueous QDs (CdS or CdTe) with the mentioned coatings were prepared. The first examples of CdTe coated with 2MPA emitting from green to red and CdTe-PAA/MAA were provided as well.Publication Metadata only A water-soluble Irgacure 2959-based diallylammonium salt system for antibacterial coatings(Wiley, 2024) Balaban, Burcu; Avci, Duygu; Department of Chemistry; Güner, Pınar Tatar; Acar, Havva Funda Yağcı; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of SciencesA water-soluble mixture of a novel diallylammonium salt photoinitiator based on 2-hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone (Irgacure 2959 or I2959) and diallylammonium tosylate has been prepared. It shows excellent water-solubility of 6.8 wt% in water, much greater than the solubility of I2959 (<2 wt%). It has a strong absorbance at 269 nm (epsilon similar to 15731) in methanol. It exhibits 15.6 times higher migration stability than I2959 due to its monomeric nature. Its photoinitiating efficiency of 2-hydroxyethylmethacrylate (HEMA) and poly(ethylene glycol) diacrylate (PEGDA, M-n = 575 D) was found to be similar to I2959. PEGDA hydrogels prepared using the synthesized photoinitiator (PI) were found to have highly porous structures (15.44 mu m) compared with those using I2959. PEGDA film prepared using this PI has demonstrated antibacterial properties against gram-negative Pseudomonas aeruginosa (ATCC 15442) and gram-positive Staphylococcus aureus (ATCC 23235) bacterial species.Publication Metadata only Acetylene-furan trimer formation at 0.37 K as a model for ultracold aggregation of non- and weakly polar molecules(Bilkent University, 2011) Metzelthin, Anja; Sánchez-García, Elsa; Schwaab, Gerhard; Thiel, Walter; Sander, Wolfram; Havenith, Martina; Department of Chemistry; Birer, Özgür; Researcher; Department of Chemistry; College of Sciences; N/AWe have studied the aggregation process of (C2H 2)⋯furan trimers at ultracold temperatures (0.37 K) in helium nanodroplets. Computational sampling of the potential energy surface using the multiple-minima-hypersurface (MMH) approach yielded seven possible minimum structures, optimized at the MP2 level of theory with the cc-pVTZ and 6-311++G(d,p) basis sets. Experimentally, we could assign five transitions in the IR spectrum of acetylene-furan aggregates in the acetylene C-H asym stretch region between 3240 and 3300 cm-1 to vibrational bands of the 2:1 acetylene-furan trimer. The transitions were assigned to three ring structures that all contain the T-shaped acetylene dimer as structural sub-motif. Two of the structures form a nonplanar ring involving a C-HAc⋯πFu bond, the third is a nearly planar ring containing a C-HAc⋯OFu bond. This assignment was corroborated by quantum mechanical/molecular dynamics (QM/MD) simulations mimicking in detail the aggregation process of precooled monomers. The simulations provided evidence for a transition from a higher level local minimum to the global minimum state over a small barrier during the aggregation process. The experimentally observed structures can be explained by a step-by-step aggregation of moieties pre-cooled to 0.37 K that are steered by intermediate and short-range electrostatic interactions. Thus, we are able to unravel a special aggregation mechanism which differs from aggregation of molecules with large dipole moments where this aggregation process is dominated by long range 1/r3 dipole-dipole interaction ("electrostatic steering"). This mechanism is expected to be a general mechanism in ultracold chemistry. Brrrr-cold! The aggregation process of (C2H 2)⋯furan trimers at ultracold temperatures (0.37 K) in helium nanodroplets is studied by a combination of computational and spectroscopic techniques. The results unravel a special aggregation mechanism for non- and weakly polar molecules, which is expected to be generally applicable in ultracold chemistry.