Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
Browse
4 results
Search Results
Article Citation - WoS: 6Citation - Scopus: 7Measuring Temperature Change at the Nanometer Scale on Gold Nanoparticles by Using Thermoresponsive PEGMA Polymers(Wiley-VCH Verlag GmbH, 2017-06-13) Yavuz, Mustafa S.; Citir, Murat; Cavusoglu, Halit; Demirel, GokhanPlasmonic heating of gold nanoparticles (AuNPs) under laser illumination is a highly desirable technique, especially for cancer therapy. However, significant drawbacks still remain including uncontrolled heat release from AuNPs, random exposure duration, and selection of the proper laser power without damaging normal healthy cells. Herein, we demonstrate a simple and versatile method to measure temperature variation on the surface of Au nanoparticles under laser irradiation based on a thermoresponsive polymer, poly(ethylene glycol) methylether methacrylate (PEGMA). In this context, a series of PEGMA polymers were synthesized to have different lower critical solution temperature (LCST) values (28-90 degrees C) and conjugated to the surface of spherical AuNPs by a gold-thiolate linkage. According to our strategy, the AuNPs first photothermally absorb light energy and convert it to heat owing to their tailored photothermal characteristics. The generated heat from the AuNPs subsequently dissipates into the surrounding thermoresponsive PEGMA polymer. When the temperature generated on the Au surface upon laser irradiation for a certain exposure time reaches the LCST value of the surrounding PEGMA polymer, the polymer chain collapses. Therefore, the hydrodynamic diameter of the PEGMA-coated AuNPs changes, which can be easily monitored by using dynamic light scattering (DLS). We systematically measured the temperature (28-90 degrees C) generated on the AuNP surfaces by using different laser power densities with varying durations. We believe that the resulting strategy will be very valuable for oncologists to easily predict the minimum laser power and duration needed to destroy the cancer cells through the photothermal effect of Au nanostructures.Article Citation - WoS: 18Citation - Scopus: 19Infrared Multiple Photon Dissociation Spectroscopy of Protonated Histidine and 4-Phenylmidazole(Elsevier, 2012-12) Citir, Murat; Hinton, Christopher S.; Oomens, Jos; Steill, Jeffrey D.; Armentrout, P. B.The gas-phase structures of protonated histidine (His) and the side-chain model, protonated 4-phenyl imidazole (PhIm), are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light generated by the free electron laser FELIX. To identify the structures present in the experimental studies, the measured IRMPD spectra are compared to spectra calculated at a B3LYP/6-311+G(d,p) level of theory. Relative energies of various conformers are provided by single point energy calculations carried out at the B3LYP, B3P86, and MP2(full) levels using the 6-311+G(2d,2p) basis set. On the basis of these experiments and calculations, the IRMPD action spectrum for H+(His) is characterized by a mixture of [N-pi,N-alpha] and [N-pi,CO] conformers, with the former dominating. These conformers have the protonated nitrogen atom of imidazole adjacent to the side-chain (N-pi) hydrogen bonding to the backbone amino nitrogen (N-alpha) and to the backbone carbonyl oxygen, respectively. Comparison of the present results to recent IRMPD studies of protonated histamine, the radical His(center dot+) cation, H+(HisArg), H-2(2+)(HisArg), and M+(His), where M+ = Li+, Na+, K+, Rb+, and Cs+, allows evaluation of the vibrational motions associated with the observed bands. (c) 2012 Elsevier B.V. All rights reserved.Article Citation - Scopus: 25Guided Ion-Beam and Theoretical Studies of the Reaction of Os+ (6d) With O2: Adiabatic and Nonadiabatic Behavior(2013-11) Hinton, Christopher S.; Citir, Murat; Armentrout, Peter B.The kinetic-energy dependence of the Os+ + O<inf>2</inf> reaction is examined using guided ion-beam mass spectrometry. The cross section for OsO+ formation from ground state Os+ (6D) is unusual, exhibiting two endothermic features. The kinetic energy dependence for OsO+ formation is analyzed to determine D<inf>0</inf>(Os +O) = 4.96 ± 0.02 eV, with the higher energy feature having a threshold 1.36 ± 0.11 eV higher in energy. This bond energy is roughly consistent with previous values determined by bracketing measurements. Formation of OsO<inf>2</inf>+ is also observed with a pressure dependent cross section, establishing that it is formed in an exothermic reaction of OsO + with O<inf>2</inf>. The nature of the bonding for OsO+ and OsO<inf>2</inf>+ is discussed and analyzed primarily using theoretical calculations at the B3LYP/def2-TZVPPD level of theory. The ground state of OsO+ is identified as either 6Σ+ or 4Π, with the latter favored once estimates of spin-orbit splitting are included. Bond energies for ground state OsO+ are calculated at this level as well as BHLYP, BLYP, BP86, and CCSD(T,full) levels along with using the Stuttgart-Dresden (SDD) and Hay-Wadt (HW+) basis sets on osmium with a 6-311+G(3df) basis on oxygen. BLYP and BP86 theoretical bond energies are higher than the experimental value, whereas B3LYP and CCSD(T,full) values are lower, and BHLYP values are much too low. Potential energy surfaces for the reaction of Os+ with O<inf>2</inf> are also calculated at the B3LYP/def2-TZVPPD level of theory and reveal that ground state Os+ (6D) inserts into O<inf>2</inf> by forming a Os+(O <inf>2</inf>) (4B<inf>2</inf>) complex which can then couple with additional surfaces to form ground state OsO<inf>2</inf>+ ( 2B<inf>1</inf>). Several explanations for the unusual dual endothermic features are explored, with no unambiguous explanation being evident. As such, this heavy metal system provides a very interesting experimental phenomenon of both adiabatic and nonadiabatic behavior. © 2013 Elsevier B.V. All rights reserved. © 2013 Elsevier B.V., All rights reserved.Article Citation - WoS: 21Citation - Scopus: 21Enhancement of Anhydrous Proton Conductivity of Poly(Vinylphosphonic Acid)-Poly(2,5 Membranes Via in Situ Polymerization(Wiley-VCH Verlag GmbH, 2014-10-16) Sen, Unal; Usta, Hakan; Acar, Oktay; Citir, Murat; Canlier, Ali; Bozkurt, Ayhan; Ata, AliPolymer electrolyte membranes (PEMs) are synthesized via in situ polymerization of vinylphosphonic acid (VPA) within a poly(2,5-benzimidazole) (ABPBI) matrix. The characterization of the membranes is carried out by using Fourier transform infrared (FTIR) spectroscopy for the interpolymer interactions, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) for the thermal properties, and scanning electron microscopy (SEM) for the morphological properties. The physicochemical characterizations suggest the complexation between ABPBI and PVPA and the formation of homogeneous polymer blends. Proton conductivities in the anhydrous state (150 degrees C) measured by using impedance spectroscopy are considerable, at up to 0.001 and 0.002 S cm(-1) for (1: 1) and (1: 2) molar ratios, respectively. These conductivities indicate signifi cant improvements (> 1000x) over the physically blended samples. The results shown here demonstrate the great potential of in situ preparation for the realization of new PEM materials in future high-temperature and non-humidified polymer electrolyte membrane fuel cell (PEMFC) applications.