SIMPLE C-13-NMR METHODS FOR QUANTITATIVE-DETERMINATIONS OF POLYFLAVONOID TANNIN CHARACTERISTICS

A simple C-13-NMR method for the quantitative determination of polyfla vonoid tannin characteristics was developed. The system is effective f or use on concentrated (25-50%) solutions of natural and modified tann ins. It allows the determination of the average degree of polymerizati on (DPBAR(n)) of the polyflavonoid, resorcinol vs. phloroglucinol prop ortion of the A-ring and catechol vs. pyrogallol proportion of the B-r ing. The results obtained are consistent with existing data determined by other techniques. The method was also tried with tannin extract th at was modified to form thermosetting adhesive intermediates, and with tannin modified by sulfonation, a common commercial modification for these materials. The results were again consistent with what was expec ted. The method affords the possibility to follow by a simple techniqu e the variations in DPBAR(n) and MBAR(n) (number-average molecular wei ght) induced by chemical modifications of polyflavonoid tannin extract s and thus to correlate them with relevant structural modifications af fecting these parameters. The method is not capable of distinguishing the relative proportions of the four important flavonoid units present in commercial polymeric tannin extract. It can only distinguish the r elative proportions of (i) (procyanidins + prodelphinidins) vs. (profi setinidins + prorobinetinidins) and (ii) (prorobinetinidins + prodelph inidins) vs. (profisetinidins + procyanidins). (C) 1995 John Wiley & S ons, Inc.