Thermally Assisted Hydrolysis and Methylation of Purified Tannins from Plants
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- 作者：Klaas G. J. Nierop ; Caroline M. Preston ; and Joeri Kaal
- 刊名：Analytical Chemistry
- 出版年：2005
- 出版时间：September 1, 2005
- 年：2005
- 卷：77
- 期：17
- 页码：5604 - 5614
- 全文大小：209K
- 年卷期：v.77,no.17(September 1, 2005)
- ISSN：1520-6882
文摘
A collection of tannins extracted from various plantspecies was subjected to thermally assisted hydrolysis andmethylation (THM) using tetramethylammonium hydroxide. The products obtained included 1,3,5-trimethoxybenzenes, derived from A rings of condensed tannins(CTs), and 1,2-dimethoxybenzene, 1,2,3-trimethoxybenzene, and derivatives as major products from the B ring.1,2,4-Tri- and two tetramethoxybenzenes were also detected in most analyses. Correlation analyses revealed thatthey were derived from the B ring, with 1,2,4-trimethoxybenzene being derived from a procyanidin (PC) B ring and1,2,3,5-tetramethoxybenzene from a prodelphinidin (PD)ring. Tannins from species that contained both CT andhydrolyzable tannin (HT) produced mainly permethylatedgallic acid moieties upon THM, and the products derivedfrom CTs were less abundant. Most likely, the ester-boundHTs are more easily transmethylated than the cleavageand methylation of the C-C and C-O linked CTs. Statistical analyses of the THM products and 13C NMR data ofthe tannins showed good correlations between the B ringhydroxylation and the di- and trimethoxybenzenes observed. Using the ratio of the methyl esters of 3,4-dimethoxybenzoic acid and 3,4,5-trimethoxybenzoic acidonly provided good correlations of the percent PC as well.Furthermore, the 1,3,5-trimethoxybenzenes may serve asgood markers of tannins in plant, soil, sediment or othersamples as analyzed by THM.