engleski

Spectroscopis studies of Schiff bases derived from 4-hidroxycoumarin

Much interest has been paid by recent investigators to the study of metal complexes of coumarins and Schiff bases since they are becoming increasingly important as bio-chemical and analytical reagents. The Schiff bases prepared by the action of aromatic aldehydes on 3-amino-4-hydroxycoumarin. The structure of the so obtained 3-arylmethylenamino-4-hydroxycoumarins (R1, Ar=Ph; R2, Ar=p-chlorophenyl; R3, Ar=2-furyl) was confirmed by IR and NMR spectroscopy. The electronic absorption spectra of the Schiff bases were studied as a function of the solvent and pH of the me-dium, at room temperature. Analysis of the spectra confirmed the presence of two tautometric forms. The equilibria of various ionic species in solutions were studied spectrophotometrically and equilibrium constants were determined. The flouroscent properites of the Schiff bases in different solutions were examined too. The effect of copper(II) on the fluorescence of R2 was studied. The fluorescence of this Schiff base, dissolved in ethanol/water (F(EtOH)=0.55) was strongly quenched by copper(II); the quenching was strongest in acid medium (pH<5) at cex=284 nm and cexm=450 nm. Decrease in the emission intensity was linearly proportional to the copper(II) con-centration in the range 5-3 ppb Cu(II), if the concentration of the Schiff base was 1.2 x 10-6 mol/dm3.

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