The use of diffusion-ordered spectroscopy and complexation agents to analyze mixtures of catechins

Mixtures of catechins, (+)-catechin (C), (-)-epicatechin (EC), (-)-epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG) have been analyzed by diffusion-ordered spectroscopy (DOSY) using liquid and high-resolution magic angle spinning (HR-MAS) NMR probes. Beta-cyclodextrin (beta-CD) and bovin serum albumin (BSA), often used as ligands in affinity chromatography, were added to the mixture of catechins to mimic chromatographic conditions and modify the average mobility. The influence of the solvent, water, dimethyl sulfoxide, methanol, acetone and acetonitrile, was also investigated. The best separation of the components was achieved with beta-CD in the liquid probe using a 15% CD3CN-85% D2O solution, and this was applied to the analysis of catechins from green tea extract. The parts of the catechin molecules having the closest contact to the BSA protein were also determined by saturation transfer difference (STD) NMR experiments.