Browsing by Author "Karapire C."

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    Photophysical and photochemical characteristics of an azlactone dye in sol-gel matrix; a new fluorescent pH indicator
    (2003) Ertekin K.; Karapire C.; Alp S.; Yenigül B.; Içli S.
    The photophysical and photochemical properties of an azlactone derivative, 4-(p-N,N-dimethylaminophenylmethylene)-2-phenyl-5-oxazolone, (DPO) in a sol-gel matrix have been examined. The fluorescence quantum yield, radiative lifetime, fluorescence lifetime, fluorescence rate constant and singlet energy values of the DPO dye were determined in a modified tetraethyl orthosilicate (TEOS) solid matrix by absorption and emission spectroscopy and obtained data were compared with the results of measurements in acetonitrile (MeCN) and tetrahydrofuran (THF) solution. The sol-gel matrix enhanced the fluorescence quantum yield (Qf=0.296) and fluorescence emission lifetime (τf=0.47 ns) compared to Qf=0.0027-0.0025 and τf=0.02-0.03 ns for solutions in MeCN and THF. The acidity constant of DPO was found to be as pKa=5.1 in the transparent sol-gel matrix. The dye doped sol-gel exhibited a pH sensitivity in pH range 3.0-7.0. © 2002 Elsevier Science Ltd. All rights reserved.
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    Study of heavy metal pollution and speciation in Buyak Menderes and Gediz river sediments
    (Elsevier Ltd, 2003) Akcay H.; Oguz A.; Karapire C.
    In this study, two economically important rivers of Turkey, Gediz and Buyuk Menderes (BM) are studied to determine their environmental pollution levels. An old analytical procedure involving sequential chemical extraction is improved and used for the partitioning of particulate trace metals (Cu, Co, Cr, Mn, Fe, Zn, Pb and Ni). Cationic and anionic Mn and Cr species with different phases are also determined by using leaching, extraction and ion exchange speciation processes. The sediment samples are analysed using graphic-furnace atomic absorption spectroscopy and differential pulse anodic stripping voltammeter. Experimental results obtained on five replicate samples of fluvial bottom surface sediments at the sampling points demonstrate that the relative standard deviation of the sequential extraction procedure is generally better than ±10%. The accuracy, determined by comparing total metal concentrations with the sum of the five sequential chemical extractions, is proved to be satisfactory. The detection limits established for three standard deviations of blank for different metals are identical and found to be 0.1mg/kg for sediment samples and 1ppb for water samples. The results show that the pollution levels are significant especially for Pb, Cr, Mn and Zn in the Gediz river and Co, Mn, and Zn in the BM river. Comparison between our results and the measurements outlined before industralization and the beginning of the intensive pesticide applications in agricultural fields (In: Broekaert et al., editors, Metal speciation in the environment, vol. 23. 1989. p. 601-11; A research on the environmental pollution in the agricultual fields and watering in the Aegean region, Ege University Research Project, No. 127 1988 (in Turkish); DSI Water Analyses Report, Ankara, 1985 (in Turkish)) show that the pollution in these rivers is probably originated from industrial, agricultural and domestic waste discharges. © 2002 Elsevier Science Ltd. All rights reserved.
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    A study on photophysical properties of some Vitamin K3 derivatives
    (2004) Hakli O.; Karapire C.; Posokhov Y.; Içli S.
    Photophysical properties of menadione sodium bisulfite (MSB), menadione nicotinamide bisulfite (MNB) and menadione dimethylpyrimidinol bisulfite (MPB) were studied in their aqueous solutions. They are oil-soluble vitamins and not naturally fluorescent, however, it is possible to gain fluorescent signal by the use of phosphate buffer solutions containing sodium dodecyl sulfate (SDS) at optimum concentration. The quantum yields of fluorescence emission, Φ f, were measured as ∼10-4, 0.0085 and 0.053 for MSB, MNB, MPB, respectively. Fluorescence quenching with Co2+ ions yielded the quenching rates of 1.7×109, 4.6×1010, and 1.5×1010 M-1 s-1 for MSB, MNB and MPB, respectively. Calculated Gibbs free energy (Δ G) values (≤-5 kcal/mol) of the compounds suggest that electron transfer could be the reason of quenching with Co2+ ions. Studied derivatives were found to give two electrons. Equilibrium constants (Keq) derived from Δ G values pointed out strong association between the pairs of MSB, MNB and MPB complexes. They were irradiated by using not only artificial Xe lamp of fluorescence spectrophotometer, but also by using direct and concentrated sunlight and degradation (%), rate constant (kp) and half-lives (t1/2) were compared. Photodegradation (%) of Vitamin K3 derivatives varied depending on the irradiation source. Photostability tests pointed out MPB as the most stable derivative. © 2004 Elsevier B.V. All rights reserved.