13C NMR experiments were performed on a Bruker Avance-400
spectrometer operating at a 13C frequency of 100.59 MHz. Acidified
tannins (100 mg) were dissolved in DMSO-d6 (0.5 ml) and
lyophilized tannins (100 mg) were dissolved in D2O (0.5 ml) with
slight heating. 13C NMR spectra were acquired at 50 ◦C in order to
reduce viscosity. 10,000 scans were collected with a pulse delay of
12 s. 13C data were processed offline using XWinNMR processing
software (Acorn NMR Inc).