A study on photophysical properties of some Vitamin K 3 derivatives

Abstract

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 Co 2+ ions yielded the quenching rates of 1.7×10 9, 4.6×10 10, and 1.5×10 10 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 Co 2+ ions. Studied derivatives were found to give two electrons. Equilibrium constants ( K eq) 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 ( 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.