Tuncer Hökelek

Bio: Tuncer Hökelek is an academic researcher from Hacettepe University. The author has contributed to research in topics: Ring (chemistry) & Crystal structure. The author has an hindex of 28, co-authored 534 publications receiving 3864 citations. Previous affiliations of Tuncer Hökelek include Anadolu University.

Phosphorus–nitrogen compounds

Abstract: The salicylic acid salts of fully substituted mono(4-fluorobenzyl)spirocyclotriphosphazenes (10–15) were prepared. The structures of these phosphazenium salts (10a–15a) were determined by elemental analyses, FTIR and 1H, 13C{1H}, 31P{1H} NMR techniques. The crystal structure of 14a was verified by X-ray diffraction analysis. The thermal properties of the salts were investigated using TG/DTA and DSC instruments. The results obtained from DSC indicated that the melting temperatures and latent heats of the compounds were in the ranges of 107.76–143.04 °C and 41.64–69.73 J g−1, respectively. The thermal stabilities of the phosphazenium salts (10a–15a) are found to be different, but they have a similar decomposition mechanism. The compounds 14a and 15a exhibit noticeable cytotoxic activity against DLD-1 cancer cells, and they seem to be good candidates for being anticancer agents. All of the compounds have an antimicrobial effect on bacterial and yeast strains within the ranges of 312–625 µM (bacterial strains) and 19.5–312 µM (yeast strains). It is found that compounds 13a–15a were most effective against yeast strains. Moreover, interactions between the salts and pBR322 plasmid DNA show that 14a and 15a cleave the DNA and decrease the intensity of form I. BamHI and HindIII digestion results demonstrate that the compounds are not bound with G/G and A/A nucleotides, respectively.

Phosphorus-nitrogen compounds. 21. Syntheses, structural investigations, biological activities, and DNA interactions of new N/O spirocyclic phosphazene derivatives. The NMR behaviors of chiral phosphazenes with stereogenic centers upon the addition of chiral solvating agents.

Abstract: The reactions of hexachlorocyclotriphosphazatriene, N3P3Cl6, with N/O-donor-type N-alkyl (or aryl)-o-hydroxybenzylamines (1a−1e) produce mono- (2a−2e), di- (3a−3d), and tri- (4a and 4b) spirocyclic phosphazenes. The tetrapyrrolidino monospirocyclic phosphazenes (2f−2i) are prepared from the reactions of partly substituted compounds (2a−2d) with excess pyrrolidine. The dispirodipyrrolidinophosphazenes (3e−3h) and trispirophosphazenes (3i−3k) are obtained from the reactions of trans-dispirophosphazenes with excess pyrrolidine and sodium (3-amino-1-propanoxide), respectively. Compounds 3a−3d have cis and trans geometric isomers. Only the trans isomers of these compounds are isolated. Compounds 3a−3h have two stereogenic P atoms. They are expected to be in cis (meso) and trans (racemic) geometric isomers. In the trans trispiro compounds (3i−3k), there are three stereogenic P atoms. They are expected to be in racemic mixtures. The stereogenic properties of 3a−3k are confirmed by 31P NMR spectroscopy upon the a...

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Principles Of Fluorescence Spectroscopy

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Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg