Study on the Structure of Mangrove Polyflavonoid Tannins with MALDI-TOF Mass Spectrometry and NMR

摘要

The properties of polyflavonoid tannins from the mangrove species depend on their structure in terms of monomer units, their mean degree of polymerization and the linkage-type between flavan-3-ol units with a considerable range of structural variation. Polyflavonoid tannins were characterized by matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS), which were too difficult to be resolved by other techniques. MALDI-TOF mass spectra of polyflavonoid tannins of four mangrove species in Rhizophoraceae, Kandelia candel, Ceriops tagal, Bruguiera cylindrica and Rhizophora apiculata showed as follows: (1) procyanidin oligomers formed by catechin/epicatechin, and catechin-3-O-rhamnoside monomers were present in great proportions; epigallocatechin and epicatechin gallate monomers were not detected; (2) the doubly linked structure of A-type procyanidins were also evident from the mass spectra of K. candel; (3) there were major differences in polyflavonoid tannin structure among mangrove species; and (4) the distribution of tannin oligomers, and the number-average degree of polymerization obtained by MALDI-TOF MS appeared to compare well with the results obtained by ~(13)C nuclear magnetic resonance (NMR) analysis.