Direct observation of non-covalent complexes formed through phosphorylated flavonoid protein interaction by electrospray ionization mass spectrometry

7-Hydroxyflavone was phosphorylated by a modified Atherton-Todd reaction and the resulting structure determined by NMR, ESI-MS/MS and elemental analysis. The electrospray ionization results showed that phosphorylated flavonoids can form non-covalent complexes with many proteins such as lysozyme, cytochrome c, bovine insulin and myoglobin, while non-covalent complexes were not detected with a mixed solution of 7-hydroxyflavone and proteins. It is deduced that phosphorylated flavonoids possess relatively strong affinities for proteins and form non-covalent complexes with proteins more easily than the unphosphorylated compounds.