3.2.1. Absorption spectroscopy
Curcumin has its absorption maximum at 429 nm in pure ethanol
(Table 4). The absorption maximum was slightly red-shifted to
436 nm in GS and MC3 (Fig. 2A). An additional peak at 370 nm was
also observed in GS which appeared as a shoulder in MC3 (Fig. 2A). In
the absence of curcumin GS did not absorb above 564 nm and MC3
did not absorb above 389 nm (Fig. 2B). Dilution of curcumin-MC3
with MilliQ water, buffer pH 8.0 or PBS resulted in a decrease in
the absorbance and a blue-shift in the absorption maximum back
to ~430 nm (Table 4). The absorbance of the similarly prepared
curcumin-GS-dilutions was barely detectable (0.001 a.u. at 430 nm; results not shown). The absorbance at ~430 nm was higher after dilution
of curcumin-MC3 in buffer than in water (not shown). Upon dilution of
the curcumin-NADES samples with ethanol the absorption maximum
wavelength appeared in between that of the pure curcumin-NADES
and the aqueous curcumin-NADES solutions (Table 4). In the case of
the curcumin-MC3 sample, an increasing amount of ethanol resulted