Results And Discussion

13-cï.s-Retinoic acid in ethanol (Fig. 1), showed a 344.5 nm absorption peak (molar extinction coefficient 3.5 x 104 M"1 cm"1) and a 487.5 nm fluorescence emission peak. The absorbance was negligible at wavelengths longer than 450 nm. Nifedipine (Fig. 2) had a relatively sharp absorption peak at 237 nm (e = 1.7 x 105 M"1 cm" ) and a much broader absorption at ca. 350 nm (£357 = 4.0 x 103 M"1 cm" ). Again, the absorbance was negligible at À. > 450 nm, while no fluorescence was detected. Chloramphenicol (Fig. 3) showed a UV spectrum with a peak at 274 nm (e = 8.5 x 102 M"1 cm"1) and no fluorescence emission, while chlorpromazine (Fig. 4) displayed a main, sharp peak, at 258 nm (e = 1.1 x 103 M"1 cm"1) and a minor peak at 311 nm (e = 4.9 x 102 M"1 cm" ). Its fluorescence emission spectrum had a single peak at 450 nm.

Table 1 Triplet state properties and singlet oxygen yields in ethanol

Drug A.max (nm) Lifetime Triplet Singlet Oxygen

(jis) Quantum Yield Quantum Yield

Chlorpromazine 460 10 0.52 0.48

RetinoicAcid 420 40 <0.02 <0.01

Absorbance Fluorescence c (ü

0 0

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