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    Öğe
    Radiation effect studies in single crystal of Trifluoroacetyl-?-Aminoisobutyric acid
    (Taylor & Francis Ltd, 2015) Baskan, M. Halim; Osmanoglu, Y. Emre; Sutcu, K.; Aydin, M.; Osmanoglu, S.
    In this study, electron paramagnetic resonance of -irradiated single crystals of N-Trifluoroacetyl--amino isobutyric acid (F3Ac-Aib-OH) was investigated at room temperature and analyzed for different orientations of the crystal in the magnetic field. The paramagnetic species in N-Trifluoroacetyl--aminoisobutyric acid was attributed to the CF2-R radical (R= CONHC(CH3)COOH). Hyperfine coupling constants and g value were also determined. In addition, the single crystal of F3Ac-Aib-OH was UV-irradiated and paramagnetic species formed was studied at room temperature. The effects of gamma irradiation on fluoroamino acid and stability were discussed.
  • [ X ]
    Öğe
    Spectral analysis and quantum chemical studies of chair and twist-boat conformers of cycloheximide in gas and solution phases
    (Elsevier, 2018) Tokatli, A.; Ucun, F.; Sutcu, K.; Osmanoglu, Y. E.; Osmanoglu, S.
    In this study the conformational behavior of cycloheximide in the gas and solution (CHCl3) phases has theoretically been investigated by spectroscopic and quantum chemical properties using density functional theory (wB97X-D) method with 6-31++G(d,p) basis set, for the first time. The calculated IR results reveal that in the ground state the molecule exits as a mixture of the chair and twist-boat conformers in the gas phase, while the calculated NMR results reveal that it only exits as the chair conformer in the solution phase. In order to obtain the contributions coming from intramolecular interactions to the stability of the conformers in the gas and solution phases, the quantum theory of atoms in molecules (QTAIM), noncovalent interactions (NCI) method, and natural bond orbital analysis (NBO) have been employed. The QTAIM and NCI methods indicated that by intramolecular interactions with bond critical point (BCP) the twist-boat conformer is more stabilized than the chair conformer, while by steric interactions it is more destabilized. Considering that these interactions balance each other, the stabilities of the conformers are understood to be dictated by the van der Waals interactions. The NBO analyses show that the hyperconjugative and steric effects play an important role in the stabilization in the gas and solution phases. Furthermore, to get a better understanding of the chemical behavior of this important antibiotic drug we have evaluated and, commented the global and local reactivity descriptors of the both conformers. Finally, the EPR analysis of gamma-irradiated cycloheximide has been done. The comparison of the experimental and calculated data have showed the inducement of a radical structure of (CH2)(2)CCH2 in the molecule. The experimental EPR spectrum has also confirmed that the molecule simultaneously exists in the chair and twist-boat conformers in the solid phase. (C) 2017 Elsevier B.V. All rights reserved.