Abstract
Novel valorization routes for tannins were opened by the development of a simple, straightforward, robust, and flexible approach to the selective functionalization of condensed and hydrolyzable tannins. Irrespective of the different degrees of polymerization, different commercial tannins were efficiently functionalized by the generation of an ether linkage bound to a short linker carrying the desired functional group. Functionalizations could be realized at varying degrees of technical loadings, i.e., amounts of introduced tannin-alien functionalities per number of phenolic hydroxyl groups. The same strategy was found suitable for the synthesis of polyethylene glycol-functionalized tannin copolymers. Condensed tannins functionalized with carboxylic acid moieties could be converted into a tannin–oligopeptide hybrid.
Highlights
Eco-friendly chemical compounds in the form of plant extracts such as polyphenolic lignins and tannins are of utmost interest with respect to both industrial and biomedical applications.[1−4] Especially, tannins represent one of the most versatile compendiums of polyphenolic compounds derived from biomass.[4,5] not as abundant as lignin, they are much more widely used in everyday life due to their relatively easy isolation and traditionally well-known, albeit not always scientifically fully elucidated/understood, functional features.[4]
These three tannins were identified as mixtures ofcatechins and fisetinidols with some gallo(epi)catechin motifs in the case of Vv and Vv-20; traces of O-gallates were found in both samples.[44]
Condensed tannins could be derivatized in basic aqueous solutions, while Lewis-acid catalysis in anhydrous DMF was applied for hydrolyzable tannins
Summary
Eco-friendly chemical compounds in the form of plant extracts such as polyphenolic lignins and tannins are of utmost interest with respect to both industrial and biomedical applications.[1−4] Especially, tannins represent one of the most versatile compendiums of polyphenolic compounds derived from biomass.[4,5] not as abundant as lignin, they are much more widely used in everyday life due to their relatively easy isolation and traditionally well-known, albeit not always scientifically fully elucidated/understood, functional features.[4]. HCl. Subsequent isolation of the functionalized tannin was achieved following one of the general protocols described below. The epoxy-terminated functional, e.g., epoxide-terminated glycidyltrimethylammonium chloride (C3-NMe3Cl), eventually dissolved in a small amount of dry DMF, was added in concentrations depending on the desired final technical loading, typically in the range from 0.1 to 0.5 equiv to tannin phenolic OH groups. Subsequent isolation of the functionalized tannin was achieved following one of the general protocols described below. Functionalized tannins were precipitated at pH 2 by adding suitable volumes of 2 N aqueous HCl and were subsequently isolated by centrifugation (15 min, 5000 rpm). Molecular weights were calculated from a linear calibration constructed with poly(styrene sulfonic acid) polymers (MW 4300−2.6 ×106 g mol−1); analyses were run in duplicate
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