Genistein complexes with amines: structure and properties

Abstract

New amine complexes of genistein in the crystal and the solution state have been studied by X-ray crystallography and by ¹H and ¹³C NMR spectroscopy. The gas-phase structures have been modelled with ab initio quantum chemical calculations. The morpholine–genistein hydrogen bonded complex has been investigated by all the above methods whereas the triethylamine, morpholine and piperazine complexes have been investigated with ¹H NOE and ¹³C NMR spectroscopy. The X-ray results show the genistein–morpholine complex to be formed as a result of proton transfer from the genistein OH group at position C7 to the morpholine nitrogen atom. This complex also has the lowest total energy when compared to other possible complexes. The NMR measurements in solution indicate that the protonated amine is in fast exchange between various interaction sites, the most stable complex being formed at position C7 as in the crystal. The ab initio quantum mechanical calculations show that this position is also the best for interactions. The ¹³C NMR chemical shifts calculated theoretically are in agreement with experimental values.