Polydopamine—An Organocatalyst Rather than an Innocent Polymer

Abstract

Polydopamine (PDA) is easily available by oxidation of dopamine and is widely used for persistent coatings of various materials. It is hitherto considered to be inert in many interesting biomedical and other applications. Results presented here, reveal an unexpected behavior of polydopamine as an organocatalyst in direct aldol reactions under mild conditions. Evidence was found for dual catalysis making use of amino and phenolic hydroxy groups found in PDA. Thus scientists must be aware that PDA is not an innocent polymer and can cause unwanted side effects in important applications, such as in biomedicine or as supports in catalysis.

Palladium on Polydopamine: Its True Potential in Catalytic Transfer Hydrogenations and Heck Coupling Reactions

“…Although the carbonyl group of acetophenone and benzophenone was possible to reduce, molecules containing aldehydes remained unaffected under the reaction conditions (Table , entry 10, and Table , entry 6). We speculated that an imine formation of the aldehydes with the amino groups of PDA could block the catalytic sites or reduce the catalytic activity in other ways.…”

“…In contrast to these desirable properties, its application is limited in catalytic organic transformations. As an organocatalyst, PDA promotes the aldol reaction between 4‐nitrobenzaldehyde and cyclohexanone owing to the presence of both acidic phenol groups and basic amino‐groups . It has been used as a catalyst in the oxidative coupling of thiols, in which its redox activity (transformation of phenolic OH groups to quinoid form) was beneficial .…”

Simultaneous enhancements of mechanical properties and hydrophilic properties of polypropylene via nano‐silicon dioxide modified by polydopamine

“…polydopamine (PDA) has emerged in recent years as a synthetic analogue of the naturally occurring melanin, which has been found extraordinary utility in a range of applications including surface coatings intermediary binding agent . polydopamine (PDA) can also form durable coating on a variety of materials, such as metals, glass, and polymers . In addition, PDA was reported as an excellent UV‐shielding polymer material, the incorporation of it can significantly increase ultraviolet resistance of plastic product …”

Polydopamine as a Catalyst for Thiol Coupling

“…[4] Lee et al inspired this mechanism [25] and opened the door to the simple and versatile modification of material surfacest hrough the oxidative formation of PDA. [26][27][28][29][30][31][32][33] Although there are still challenges to clarify the chemical structure of synthetic PDA, it is generally agreedthat dopamine must be oxidized into dopamine quinone and that there are abundant quinone motifs in the corresponding polymer. [34][35][36] These mechanismsh aveb een summarized by d'Ischia et al [37] Therefore, it is reasonable for us to develop abiomimeticr oute for the synthesis of disulfides by using the quinone motifs in PDA.…”