Phytochemistry

The term ‘tannin’ was first applied by Seguin in 1796 to denote sub-stances present in plant extracts which were able to combine with pro-tein of animal hides, prevent their putrefaction and convert them into leather. On this basis a tannin is a substance which is detected quali-tatively by a tanning test (the goldbeater’s skin test) and is determined quantitatively by its adsorption on standard hide powder. This defini-tion excludes simpler phenolic substances, often present with tannins, such as gallic acid, catechins and chlorogenic acid, although they may under certain conditions give precipitates with gelatin and be partly retained by hide powder. Such substances of relatively low molecular weight are called ‘pseudo-tannins’. Most true tannins have molecu-lar weights of from about 1000 to 5000. To be effective for tannage the polyphenol molecule most be neither so large as to be unable to enter the interstices between the collagen fibrils of the animal skin nor so small that it is unable to cross-link between the protein molecules of adjacent fibrils at several points. Many tannins are glycosides. The definition of a tannin as given above is an old, essentially practical one which may be purely fortuitous and, in the light of further research, could prove misleading from the point of view of plant metabolism and plant biochemistry. Indeed, modern authors often treat tannins not as a specific phytochemical group but as examples of polyphenols illustrat-ing particular aspects of gallic acid and flavan-3-ol phytochemistry. The characteristic properties of tannins derive from the accumulation within a moderately sized molecule of a substantial number (1–2 per 100 mol. wt.) of phenolic groups many of which are associated with o-dihydroxy and o-trihydroxy orientation within a phenyl ring. Capsaicin Capsaicin derivate dimer HO MeO O N H N H HO HO MeO MeO O O O O branched sugar chain Capsianoside structure branched sugar chain N H Fig. 21.5 Some constituents of capsicum. www.konkur.in

What core structure do anthraquinones typically possess?

Which of the following is NOT a known laxative plant associated with anthraquinone?

Which forms can anthraquinones be found in nature?

What historical use is associated with anthraquinone-containing plants?

Dianthrones are formed from the union of how many anthrone units?