Publications without Fulltext
Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
Browse
91 results
Filters
Advanced Search
Filter by
Settings
Search Results
Publication Metadata only Collision-induced state-changing rate coefficients for cyanogen backbones NCN 3Σ− and CNN 3Σ− in astrophysical environments(Royal Society of Chemistry, 2023) González-Sánchez, Lola; de la Fuente, Jorge Alonso; Sanz-Sanz, Cristina; Wester, Roland; Gianturco, Francesco A.; Department of Chemistry; Department of Chemistry; College of SciencesWe report quantum calculations involving the dynamics of rotational energy-transfer processes, by collision with He atoms in interstellar environments, of the title molecular species which share the presence of the CN backbone and are considered of importance in those environments. The latter structural feature is taken to be especially relevant for prebiotic chemistry and for its possible role in the processing of the heterocyclic rings of RNA and DNA nucleobases in the interstellar space. We carry out ab initio calculations of their interaction potentials with He atoms and further obtain the state-to-state rotationally inelastic cross sections and rate coefficients over the relevant range of temperatures. The similarities and differences between such species and other similar partners which have been already detected are analyzed and discussed for their significance on internal state populations in interstellar space for the two title molecular radicals.Publication Metadata only Antibacterial silicone-urea/organoclay nanocomposites(Springer, 2009) Department of Chemistry; N/A; N/A; Department of Chemistry; Yılgör, Emel; Nugay, Işık Işıl; Bakan, Murat; Yılgör, İskender; Researcher; Undergraduate Student; Undergraduate Student; Faculty Member; Department of Chemistry; College of Sciences; College of Engineering; College of Engineering; College of Sciences; N/A; N/A; N/A; 24181Montmorillonite modified with distearyldimethyl ammonium chloride (C18-QAC) (Nanofil-15) (NF15) was incorporated into polydimethylsiloxane-urea (silicone-urea, PSU) copolymers. PSU was obtained by the reaction of equimolar amounts of aminopropyl terminated polydimethylsiloxane (PDMS) oligomer (= 3,200 g/mol) and bis(4-isocyanatohexyl) methane (HMDI). A series of PSU/NF15 nanocomposites were prepared by solution blending with organoclay loadings ranging from 0.80 to 9.60% by weight, corresponding to 0.30 to 3.60% C18-QAC. Colloidal dispersions of organophilic clay (NF15) in isopropanol were mixed with the PSU solution in isopropanol and were subjected to ultrasonic treatment. Composite films were obtained by solution casting. FTIR spectroscopy confirmed that the organoclay mainly interacted with the urea groups but not with PDMS. XRD analysis showed that nanocomposites containing up to 6.40% by weight of organoclay had fully exfoliated silicate layers in the polymer matrix, whereas 9.60% loading had an intercalated structure. Physicochemical properties of nanocomposites were determined. PSU/NF15 nanocomposites displayed excellent long-term antibacterial properties against E. coli.Publication Metadata only Nanoparticle based induction heating at low magnitudes of magnetic field strengths for breast cancer therapy(Elsevier, 2019) Zuvin, Merve; Koçak, Muhammed; Akkoç, Yunus; Kutlu, Özlem; Gözüaçık, Devrim; Koşar, Ali; N/A; Department of Chemistry; Ünal, Özlem; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178902Magnetic hyperthermia has received much attention during the last decade due to its implementation in cancer treatment. Recently, functionalized superparamagnetic iron oxide nanoparticles (SPION) emerged as a strong alternative adjuvant treatment approach, which complements conventional methods such as chemotherapy. In this study, we demonstrate the anticancer effect of Poly(acrylic acid)-coated, anti-HER2-tagged SPIONs on breast cancer cells using a low magnetic field strength of 0.8 kAm(-1), which is significantly lower compared to the literature, with a frequency of 400 kHz. Specificity was achieved via anti-HER2 antibody attachment to nanoparticles. HER2-positive SKBR3 and MDA-MB-453 cell lines internalized the nanoparticles successfully. These nanoparticles, which were not toxic to these cell lines, led to a prominent decrease in cell proliferation and survival in MDA-MB-453 cells when subjected to hyperthermia. Therefore, the hyperthermia-targeted SPION approach could be developed as a potential cancer treatment approach against breast cancer and possible other cancer types.Publication Metadata only Reversible switching of wetting properties and erasable patterning of polymer surfaces using plasma oxidation and thermal treatment(Elsevier Science Bv, 2018) Soydan, Seren; Jonas, Alexander; N/A; Department of Chemistry; N/A; Department of Chemistry; Department of Physics; Department of Chemistry; Rashid, Muhammed Zeeshan; Atay, İpek; Yağcı, Mustafa Barış; Yılgör, Emel; Kiraz, Alper; Yılgör, İskender; PhD Student; Post Doctorate Student; Researcher; Researcher; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; N/A; College of Sciences; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; N/A; N/A; 40527; 22542; 24181Polymer surfaces reversibly switchable from superhydrophobic to superhydrophilic by exposure to oxygen plasma and subsequent thermal treatment are demonstrated. Two inherently different polymers, hydrophobic segmented polydimethylsiloxane-urea copolymer (TPSC) and hydrophilic poly(methyl methacrylate) (PMMA) are modified with fumed silica nanoparticles to prepare superhydrophobic surfaces with roughness on nanometer to micrometer scale. Smooth TPSC and PMMA surfaces are also used as control samples. Regardless of their chemical structure and surface topography, all surfaces display completely reversible wetting behavior changing from hydrophobic to hydrophilic and back for many cycles upon plasma oxidation followed by thermal annealing. Influence of plasma power, plasma exposure time, annealing temperature and annealing time on the wetting behavior of polymeric surfaces are investigated. Surface compositions, textures and topographies are characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and white light interferometry (WLI), before and after oxidation and thermal annealing. Wetting properties of the surfaces are determined by measuring their static, advancing and receding water contact angle. We conclude that the chemical structure and surface topography of the polymers play a relatively minor role in reversible wetting behavior, where the essential factors are surface oxidation and migration of polymer molecules to the surface upon thermal annealing. Reconfigurable water channels on polymer surfaces are produced by plasma treatment using a mask and thermal annealing cycles. Such patterned reconfigurable hydrophilic regions can find use in surface microfluidics and optofluidics applications. (C) 2018 Elsevier B.V. All rights reserved.Publication Metadata only Chaos in rotating triatomic clusters(Editions Physique, 1997) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Lyapunov exponent distributions of rotating triatomic Lennard-Jones clusters are calculated to analyze the effects of the vibrational and rotational motion on the extent of chaotic behavior. Initial momentum components are assigned to atoms either to rotate the clusters around symmetry axes or to generate random angular momenta. In both cases, it is seen that the initial kinetic energy assigned to vibrational modes is the dominant factor which determines the degree of chaos.Publication Metadata only Pi-stack dimers of small polyaromatic hydrocarbons: a path to the packing of graphenes(Amer Chemical Soc, 2009) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129MP2 calculations of the stacking energy are reported for the dimers of a set of polycyclic aromatic hydrocarbons. The interaction strengths and their dependence on the shape-dependent measures as well as the aromatic character of the monomer are studied. For small systems involving four to six rings, the noncovalent interactions seem to be independent of the shape of the monomers. The most preferred conformations for parallel stacked dimers are not aligned exactly but off-center with small shifts; however, these shifts are on the order of 1 angstrom, and the energy necessary to keep them aligned is less than 0.5 kcal/mol per ring. Small-angle rotations within the molecular planes also do not require much energy, and in some cases they lead to stronger interactions.Publication Metadata only The effect of nanoparticles on the surface hydrophobicity of polystyrene(Springer, 2008) N/A; Department of Chemistry; Yüce, Mehdi Yavuz; Demirel, Adem Levent; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 6568The surface hydrophobicity of polystyrene-nanoparticle nanocomposites has been investigated as a function of the nanoparticle content. The addition of hydrophobically coated nanoparticles in polystyrene increased the contact angle θ of a water drop with respect to that on polystyrene surface due to change of surface composition and/or surface roughness. When the nanoparticles dispersed well in the polymer, cos θ decreased linearly with increasing amount of nanoparticles indicating a composite surface consisting of smooth polystyrene regions and rough nanoparticle regions. In case of formation of nanoparticle aggregates in polystyrene, cos θ decreased sharply at a critical concentration of nanoparticles. The observed behaviour was modeled in terms of a transition from Wenzel regime to Cassie-Baxter regime at a critical roughness length scale below which the Laplace pressure prevented the penetration of the water drop into the surface undulations. We argue that multiple length scales are needed below the critical roughness length scale to increase the contact angle further by decreasing the fraction of surface area of solid material (increasing the fraction of surface area of air) underlying the water drop.Publication Metadata only Quenching vibrations of cesium dimers by He at low and ultralow temperatures: quantum dynamical calculations(Springer, 2011) Caruso, D.; Tacconi, M.; Bovino, S.; Gianturco, F. A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129This paper analyses in detail the energy redistribution from the upper vibrational levels of Cs dimers, thought to be obtained from initial recombination processes that generate excited internal states of the triplet configuration (3) I pound (u) (+) . Their quenching is examined as they are made to further collide with (4)He buffer gas at temperatures below and around 100 mK. The relevant cross sections are computed by using a multichannel quantum dynamical approach and employ a full, ab initio potential energy surface. Due to their smallness (see Ref. [R.B. Ross, J.M. Powers, T. Atashroo, W.C. Ermler, I.A. LaJohn, P. Christiansen, J. Chem. Phys. 93, 6654 (1999)]) the fine structure effects have not been explicitly included in this study. The final, cumulative cross-sections are discussed and analyzed in terms of the overall quenching behavior shown by different initial states of the dimer and in terms of the changing ratios between collisional cooling and vibrational quenching cross sections as a function of trap temperature. The corresponding quenching rates are also computed and analysed.Publication Metadata only The isotope effect of boron on the carbon doping and critical current density of (MgB2)-B-11 superconductors(Royal Society of Chemistry (RSC), 2017) Cheng, Fang; Liu, Yongchang; Ma, Zongqing; Al Hossain, M. Shahriar; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882Previous works mainly focused on the isotope effect of boron on the Tc performance and superconducting mechanism of MgB2 superconductors but were never concerned with its effect on the chemical doping and critical current density (J(c)) performance of MgB2, which is of great importance in terms of electromagnetic applications. In the present work, the isotope effect of B-11 on carbon doping and Jc of MgB2 superconductors was for the first time studied systemically. It is found that as the chemical activity of B-10 is higher than B-11, the substitution of B by C can more easily occur on B-10 than on the B-11 site of the MgB2 lattice. This is why carbon doping fails to increase the Jc value of isotope (MgB2)-B-11 superconductors. Our result is quite different from the case in carbon doped normal MgB2 superconductors with a natural boron source (composed of B-10 -18.98% and B-11 -81.02%) reported in most previous studies, where C can substitute a part of B-10 and thus significantly improve Jc performance at high fields. Our results provide a deeper understanding on the boron isotope effect and chemical doping mechanism in MgB2 superconductors.Publication Metadata only Lyapunov instability in rotating systems from ergodic molecular dynamics simulations(Elsevier Science Bv, 2000) Calvo, Florent; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129We improve the classical molecular dynamics (MD) method by a J-walking microcanonical Monte Carlo (MC) scheme to overcome broken ergodicity. This MC method rigorously samples the MD ensemble at finite energy and angular momentum. It is illustrated on the nonlinear dynamics of a 13-atom Lennard-Jones cluster.