Browsing by Subject "sunlight"

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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.
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    Stable spiro-endoperoxides by sunlight-mediated photooxygenation of 1,2-O-alkylidene-5(E)-eno-5,6,8-trideoxy-α-D-xylo-oct-1,4-furano-7-uloses
    (2005) Çetin F.; Yenil N.; Yüceer L.
    Sunlight-mediated photooxygenation of 3-O-acetyl and 3-O-methyl derivatives of 1,2-O-alkylidene-5(E)-eno-5,6,8-trideoxy-α-D-xylo-oct-1,4-furano-7- uloses (1a-e) in carbon tetrachloride solution gave stable 4,7-epidioxy derivatives in 4R (2a-e) and 4S (3a-e) configurations. The presence of an endo alkyl, on the 1,2-O-alkylidene group and its size, resulted in an increase of the yield of the 4S isomers. 3-O-Acetyl derivatives yielded products as a mixture of C-7 anomers, whereas 3-O-methyl derivatives gave pure single stereoisomers. © 2005 Elsevier Ltd. All rights reserved.