Willow bark proanthocyanidins with potential for water treatment: Chemical characterization and zinc/bisphenol A removal

This study investigates the chemical structure of proanthocyanidin-rich crude extracts from willow bark and these materials were tested initially as adsorbents for artificial (waste)water treatment. The crude extracts were obtained through mild water extraction and the colorant fractions were further chromatographically fractionated to understand the chemical structure of the willow bark proanthocyanidins. The chemistry of crude extracts and purified fractions were investigated using nuclear magnetic resonance (NMR) and ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Both NMR (liquid and solid-state) and UPLC-MS/ MS suggest that the crude extracts constitute of interflavan linked flavan-3-ols, i.e. proanthocyanidins with both procyanidin (PC)-type and prodelphinidin (PD)-type subunits, with the PC/PD ratio of approximately 2.3-2.5. PD-type proanthocyanidins were detected from the purified colorant fractions only with UPLC-MS/MS. Both the UPLC-MS/MS and size exclusion chromatography suggest that the crude extracts have an average oligomerization degree of roughly 5-6 flavan-3-ol units. Adsorption experiments showed that the activated foams made of crude extracts were effective in removing both zinc and Bisphenol A (BPA) with removal effi-ciencies of roughly 80-90% and thus these willow bark-derived proanthocyanidins are promising in water treatment. The significance of this study suggests the upgrading use of crude extracts for water treatment could significantly improve the value of willow bark.

Automated summary

This study examined the chemical structure of proanthocyanidin-rich crude extracts from willow bark and tested their adsorption capabilities for water treatment. NMR and UPLC-MS/MS analysis suggest that the crude extracts contain interflavan linked flavan-3-ols, including both procyanidin (PC)-type and prodelphinidin (PD)-type subunits. Adsorption experiments showed that activated foams made of the crude extracts effectively removed zinc and Bisphenol A (BPA) from water. The findings highlight the potential of willow bark-derived proanthocyanidins for water treatment.