A study on photophysical properties of some Vitamin K3 derivatives
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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, Phi(f), were measured as similar to10(-4), 0.0085 and 0.053 for MSB, MNB, MPB, respectively. Fluorescence quenching with Co2+ ions yielded the quenching rates of 1.7 x 10(9), 4.6 x 10(10), and 1.5 x 10(10) M-1 s(-1) for MSB, MNB and MPB, respectively. Calculated Gibbs free energy (DeltaG) values (less than or equal to-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 (K-eq) derived from DeltaG 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 (k(p)) and half-lives (t(1/2)) were compared. Photodegradation (%) of Vitamin K-3 derivatives varied depending on the irradiation source. Photostability tests pointed out MPB as the most stable derivative. (C) 2004 Elsevier B.V. All rights reserved.