Polyphenols molecular size

Boettcher AA, Targett NM (1993) Role of polyphenolic molecular size in reduction of assimilation efficiency in Xiphister mucosus. Ecology 74 891-903 Brand TE (1976) Trophic relationships of selected benthic marine invertebrates and foraminifera in Antarctica. Antarctic J US 11 24-26... 

Boettcher, A. A., The role of polyphenolic molecular size in the reduction of assimilation efficiency in some marine herbivores. Master s thesis, University of Delaware, Newark, Delaware, 1992. 

Since the 1950s, many efforts have been made to isolate polyphenols directly from black tea, and the structures of the major phenolic compounds characteristic of fermented tea have been elucidated." ° However, the composition of black tea polyphenols is so complex that the minor phenolic substances, which cumulatively account for a substantial portion of black tea polyphenols, are difficult to separate even by high-performance liquid chromatography (HPLC). This difficulty associated with the purification is mainly due to the presence of uncharacterized substances that are detected as a broad hump on the baseline during HPLC analysis but do not produce any clear spots on thin-layer chromatography. These snbstances are probably a complex mixture of catechin oxidation products with higher molecular sizes, and usually account for the majority of black tea polyphenols. 

Polyphenols (syn vegetable tannins - proanthocya-nidins and esters of gallic acid, vide supra) constitute one of the most distinctive groups of higher plant secondary metabolites. Their uniqueness lies not only in their molecular size and polyphenolic character but also in their ability to complex strongly with proteins, carbohydrates, nucleic acids and alkaloids. Studies of these properties are not only of intrinsic scientific interest. a scientist who confesses to an interest in polyphenols is invariably asked one question - why do plants form them ... 

Polyethylene oxides and amyloses (Mr > 4000) readily complex with polyphenols but quantitative studies have been severely limited by the availability of water-soluble polysaccharides with clearly defined molecular characteristics. Semi-quantitative studies show that the association of polyphenols with polysaccharides is - in contrast to that with proteins - broadly independent of pH. Molecular size and flexibility are likewise critical factors but, significantly, where the polysaccharide can sequester the hydrophobic aryl residues of the polyphenol - holes in a crystal lattice (cellulose) or hydrophobic cavities (amylose and polysaccharide gels) - then complexation is substantially enhanced. Open, flexible, filamentous polysaccharides, such as the l-a-6-dextrans conversely bind phenolic substrates very poorly. It is interesting to note that model polysaccharide holes - in the form of the a- and 3- cyclodextrins - can sequester the aryl residues of certain polyphenols in the core of the molecule. In doing... 

Further examples of this type of polyphenolic structure in which molecular complexity and size are increased by oxidative coupling of two or more glucose derivatives (45-49) by formation of new C-0 bonds have been described, 0-62... 

To separate the plant material from the extract, centrifugation for 15-20 min at 20,000-25,000 g is applied [126]. Ultraliltration can also be used for separation of pol3 phenols however, it depends on the particle size of the polyphenolic molecules. Generally, particles with a molecular weight of 3,000-100 kDa and higher can be separated using the regular ultrafiltration membranes [36]. 

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