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ALTUN, ZİKRİ

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ALTUN

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ZİKRİ

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2012 - 20193
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Start date: 2010 × Subject: AB-INITIO ×

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    Photophysical and Analyte Sensing Properties of Cyclometalated Ir(III) Complexes
    (SPRINGER/PLENUM PUBLISHERS, 2012) ALTUN, ZİKRİ; Leavens, Bethany B. H.; Trindle, Carl O.; Sabat, Michal; Altun, Zikri; Demas, James N.; DeGraff, B. A.
    The synthesis of some heteroleptic, cyclometalated iridium(III) complexes is described. The utility of these [Ir(ppy)(2)(N-N)]Cl (ppy=2-phenylpyridine and N-N=substituted bipyridine, biquinoline, or phenanthroline) complexes as luminescence-based sensors is assessed. The emission intensity of an Ir(III) complex featuring the 3,3'-H(n)dcbpy ligand (H(n)dcbpy=dicarboxylic acid-2,2'-bipyridine; n=0,1,2 to indicate deprotonated, mono-and diprotonated species, respectively) is seen to increase in the presence of Pb(II). Insight into the structure and analyte-sensing capability is achieved by X-ray crystallography in conjunction with computational modeling. Complexes incorporating carboxylic acid-functionalized bipyridine and biquinoline as the polypyridyl ligand show pH sensitivity while similar phenanthroline complexes do not.
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    Computational thermochemistry of glycolaldehyde
    (WILEY, 2013) BLEDA, ERDİ ATA; Bleda, Erdi A.; Yavuz, Ilhan; Altun, Zikri; Trindle, Carl
    We use a variant of the focal point analysis to refine estimates of the relative energies of the four low-energy torsional conformers of glycolaldehyde. The most stable form is the cis-cis structure which enjoys a degree of H-bonding from hydroxyl H to carbonyl O; here dihedral angles 1 (OCCO) and 2 (CCOH) both are zero. We optimized structures in both CCSD(T)/aug-cc-pVDZ and aug-cc-pVTZ; the structures agree within 0.01 angstrom for bond lengths and 1.0 degrees for valence angles, but the larger basis brings the rotational constants closer to experimental values. According to our extrapolation of CCSD(T) energies evaluated in basis sets ranging to aug-cc-pVQZ the trans-trans form (180 degrees, 180 degrees) has a relative energy of 12.6 kJ/mol. The trans-gauche conformer (160 degrees, +/- 75 degrees) is situated at 13.9 kJ/mol and the cis-trans form (0 degrees, 180 degrees) at 18.9 kJ/mol. Values are corrected for zero point vibrational energy by MP2/aug-cc-pVTZ frequencies. Modeling the vibrational spectra is best accomplished by MP2/aug-cc-pVTZ with anharmonic corrections. We compute the Watsonian parameters that define the theoretical vibrational-rotational spectra for the four stable conformers, to assist the search for these species in the interstellar medium. Six transition states are located by G4 and CBS-QB3 methods as well as extrapolation using energies for structures optimized in CCSD(T)/aug-cc-pVDZ structures. We use two isodesmic reactions with two well-established thermochemical computational schemes G4 and CBS-QB3 to estimate energy enthalpy and Gibbs energy of formation as well as the entropy of the gas phase system. Our extrapolated electronic energies of species appearing in the isodesmic reactions produce independent values of thermodynamic quantities consistent with G4 and CBS-QB3. (c) 2013 Wiley Periodicals, Inc.
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    Production of Carbamic Acid Dimer from Ammonia-Carbon Dioxide Ices: Matching Observed and Computed IR Spectra
    (MDPI, 2019-04-23) BLEDA, ERDİ ATA; Altun, Zikri; Bleda, Erdi; Trindle, Carl
    The production of complex molecules in ammonia-carbon dioxide ices is presumed to pass through species of formula H3N:CO2 with further addition of ammonia and carbon dioxide. One possible landmark, carbamic acid, H2NCOOH, has been implicated among the products of warming and irradiation of such ices. Experimental study of the IR spectra of residues has suggested the presence of related species, including weakly bound 1:1 and 2:1 complexes of ammonia with carbon dioxide, zwitterionic carbamic acid, ammonium carbamate, and the dimer of carbamic acid. We computed the energetics and vibrational spectra of these species as well as the complex between ammonia and carbamic acid for gas and condensed phases. By means of a new spectrum-matching scoring between computed and observed vibrational spectra, we infer species that are most probably present. The leading candidates are ammonium carbamate, the carbamic acid-ammonia complex, and the carbamic acid dimer.