Spectroscopic Properties of Some Metal Complexes of Gossypol

The spectroscopic properties of a number of important metal—gossypol complexes have been studied and compared with those of 2-hydroxy-1-naphthaldehydes. Gossypol and its derivatives exhibit three bands, α, β, and p. The α- and β-bands are assigned to π → π* transitions and the p-band to electronic transition from highest-occupied to lowest-unoccupied molecular orbital. In the complexes, the α-band is shifted to longer wavelengths and the p-band disappears. The infrared spectra of gossypol exhibits a strong band at 6.1 μ (C—O stretching); but in the complexes, this band disappears and a new band at 5.7 μ appears. The infrared data on 2-hydroxy-1-naphthaldehyde-anthranilic acid indicates that carbonyl groups are involved in a salt-type linkage (dimer) with copper atoms. Electronic absorption spectra of several Schiff-base complexes of 2-hydroxy-1-naphthaldehyde, in conjunction with magnetic susceptibility data, are evaluated to draw conclusions on the structure of gossypol complexes.