Reversible Catechol Interactions

Catechol is a unique and versatile adhesive molecule capable of forming reversible physical interactions and irreversible covalent bonds (Figure 10.2). In this section, various catechol chemical interactions are introduced. Additionally, various chemical modifications used to modulate catechol side chain reactivity and in the preparation of catechol-functionalized polymers are reviewed. 

The close electrochemical relationship of the simple quinones, (2) and (3), with hydroquinone (1,4-benzenediol) (4) and catechol (1,2-benzenediol) (5), respectively, has proven useful in ways extending beyond their offering an attractive synthetic route. Photographic developers and dye syntheses often involve (4) or its derivatives (10). Biochemists have found much interest in the interaction of mercaptans and amino acids with various compounds related to (3). The reversible redox couple formed in many such examples and the frequendy observed quinonoid chemistry make it difficult to avoid a discussion of the aromatic reduction products of quinones (see Hydroquinone, resorcinol, and catechol). 

One of the clearest pieces of evidence for the reversibility of some covalent interactions came from the work of Gunther Wulff at the University of Dusseldorf, Germany [172], He used imprinted polymers of o-aminomethyl phenylboronic acids as chromatographic stationary phases for the separation of saccharides. Older studies [173] also point to the reversible nature of the boronic acid-saccharide interaction. The pioneering studies of fluorescent transduction of this phenomenon by Czarnik and Yoon [174] (Ohio State University), Aoyama et al. [175] (Kyushu University, Japan), and Shinkai et al. [176] (Kyushu University, Japan) have been reviewed previously [9], Our concern in this review is particularly with the systems that clearly involve PET. Czarnik and Yoon s 93 [177] which interacts with catechol derivatives to produce 94 also belongs here. It... 

An interaction of ephedrine with entacapone, a specific, reversible, peripherally acting inhibitor of catechol-O-methyl transferase, has been reported (37). 

Figure 10.2 The catechol side chain of DOPA is capable of forming reversible interactions and irreversible covalent bonds. The benzene ring of the catechol is capable of n-n interactions (A). Catechol -OH groups can function both as a hydrogen bond donor and acceptor (B). Catechol forms strong coordination complexes with metal ions (C). When catechol is oxidized to form highly reactive quinone (D), it can undergo dimer formation (E) and subsequently polymerize into oligomers. Quinone can form intermolecular crosslinking with nucleophile such as -NH2 through Schiff base substitution (F) and Michael-type addition (G).

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