3.2.2. Fluorescence spectroscopy
The fluorescence maximum of curcumin in undiluted GS and MC3
was quite similar (Table 4), although the intensity was approximately
20-fold higher in MC3. Fluorescence spectra of curcumin-GS samples
after dilution in aqueous media could not be obtained. The fluorescence
maximum of curcumin was blue-shifted after dilution of curcumin-MC3
in MilliQ water (1:10) and red-shifted after dilution of curcumin-MC3 in
MilliQ water (1:50), in the buffers and in sulfuric acid compared to a solution in pure ethanol. The fluorescence maximum of curcumin-MC3 diluted 1:10 in phosphate buffer (pH 8) and in PBS was observed only as a
shoulder in the similarly diluted sample in water. The fluorescence
maximum of curcumin-MC3 after dilution 1:50 in MilliQ water
approached the maximum of the samples diluted in the buffer solutions.
The fluorescence maximum of curcumin-MC3 and curcumin-GS
diluted in ethanol appeared in between the pure curcumin-NADES
(570–574 nm) and the pure ethanol solution (548 nm; Table 4). The
fluorescence intensity of curcumin-MC3 (AUCfl divided by the absorbance and multiplied with the dilution factor) increased in a linear
fashion (r N 0.99) with increasing amounts of ethanol (Fig. 5). The fluorescence intensity of curcumin-GS (AUCfl divided by the absorbance and
multiplied with the dilution factor) increased between 0–20% (v/v)
ethanol, showed nearly any increase between 20–50% (v/v) ethanol
and then increased above 50% (v/v) ethanol (Fig. 5). The slope of the
curve (fluorescence vs. concentration of ethanol) appeared similar in
the samples of CS-curcumin and MC3-curcumin above 50% (v/v)
ethanol (Fig. 5).