3.9. Electronic spectrum
The ultraviolet-visible spectra of S(-) and R(+) forms of CQ were
predicted in aqueous solution with the time-dependent DFT calculations
(TD-DFT) and they are compared in Figure 8 with the
corresponding experimental in methanol solution taken from Ref [1].
The same curves obtained for the two S(-) and R(‘+) forms could indicate
the presence of both enantiomers in solution, in accordance to the
experimental UV-Vis spectrum and to the 1H- and13C-NMR studies. In the experimental UV-Vis spectrum
recorded between 200 to 400 nm are observed maxima at 218, 253 and 328
nm and minima at 243 and 275 nm while the predicted visible absorption
wavelengths and oscillator strength (f ) for both enantiomers of
chloroquine can be observed in Table S11 . The positions of
these bands are in agreement with those observed in other quinoline
compounds [80]. The different bands observed in the experimental
spectrum can be associated to the different transitions predicted by NBO
calculations in aqueous solution, as detailed in Table S4. The different
observed bands can be assigned to n→π* , π→π* , n→σ*and σ→σ* transitions predicted by NBO calculations with higher
energy values.