Coordination of aluminium with purpurogallin and theaflavin digallate

Polyphenols are antioxidants, which are known to influence bioavailability of metals in the body. The theaflavins of black tea are important members of this family, which have been sparsely investigated. The complexation of aluminium with purpurogallin (2,3,4,6-tetrahydroxy-5H-benzocyclohepten-5-one) has been investigated using nuclear magnetic resonance (NMR) spectroscopy, liquid chromatography-mass spectroscopy (LC-MS) and Fourier transform infrared (FT-IR) spectroscopy. 1H NMR was used to determine the coordination site of the aluminium ion and LC-MS to determine the stoichiometry and molecular weight of the major complex formed in solution. FT-IR spectral comparisons were used to corroborate the proposed chelating moiety. The complexation of aluminium with the high-molecular-weight, tea polyphenol theaflavin digallate was also investigated using 1H NMR and heteronuclear multiple quantum coherence experiments. Structures of the major aluminium purpurogallin and aluminium theaflavin digallate complexes are proposed.