Tannic Acid Radicals in the Presence of Alkali Metal Salts and Their Impact on the Formation of Silicate-Phenolic Networks.

Florian Weber,Einar Sagstuen,Tian Zheng,Qi-Zhi Zhong,Hanna Tiainen

doi:10.1021/acsami.0c16946

Florian Weber, Einar Sagstuen + Show 3 more

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https://doi.org/10.1021/acsami.0c16946

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Abstract

Polyphenolic molecules have become attractive building blocks for bioinspired materials due to their adhesive characteristics, capacity to complex ions, redox chemistry, and biocompatibility. For the formation of tannic acid (TA) surface modifications based on silicate-phenolic networks, a high ionic strength is required. In this study, we investigated the effects of NaCl, KCl, and LiCl on the formation of TA coatings and compared it to the coating formation of pyrogallol (PG) using a quartz-crystal microbalance. We found that the substitution of NaCl with KCl inhibited the TA coating formation through the high affinity of K+ to phenolic groups resulting in complexation of TA. Assessment of the radical formation of TA by electron paramagnetic resonance spectroscopy showed that LiCl resulted in hydrolysis of TA forming gallic acid radicals. Further, we found evidence for interactions of LiCl with the Siaq crosslinker. In contrast, the coating formation of PG was only little affected by the substitution of NaCl with LiCl or KCl. Our results demonstrate the interaction potential between alkali metal salts and phenolic compounds and highlight their importance in the continuous deposition of silicate-phenolic networks. These findings can be taken as guidance for future biomedical applications of silicate-phenolic networks involving monovalent ions.

Highlights

Derived polyphenolic molecules have attracted great interest in creating novel and sustainable biomaterials based on green chemistry.[1−5] Their versatile interaction with interfaces originates from their molecular structure featuring catechol and galloyl groups that present an opportunistic reaction site for metal coordination and surface adhesion
Since the oxidation in alkaline condition is strongly dependent on the oxygen update,[15] we investigated the radical formation under varying O2 uptake
We investigated the potential of salts to interact with Siaq inhibiting the formation of silicate-phenolic networks by blocking silicic acid. 29Si Nuclear Magnetic Resonance (NMR) experiments of 0.1 M Siaq showed a major peak for silicic acid (Q0) followed by minor peaks of Si polycondensates with Q1 and Q2 states (Figure S26).[61]

Summary

Introduction

Derived polyphenolic molecules have attracted great interest in creating novel and sustainable biomaterials based on green chemistry.[1−5] Their versatile interaction with interfaces originates from their molecular structure featuring catechol and galloyl groups that present an opportunistic reaction site for metal coordination and surface adhesion. The self-assembly and deposition process of polyphenolic layers depend on the type of polyphenol.[12] While tannic acid (TA) layers are commonly obtained through interaction with metal ions creating metal-phenolic networks (MPNs),[13] flavonoids, and low molecular weight polyphenols, such as dopamine and pyrogallol (PG), rely on oxidative polymerization.[14] Oxidation of phenolic molecules by dissolved oxygen results in their respective quinone form and is usually controlled by the solution pH.[15,16] Via oxidant induction or control of the pH, the coating formation of polyphenolic molecules can be regulated.[7,17] diverse secondary interactions, such as π-stacking, π-cation interaction, hydrogen bonding, and electrostatic interactions affect the intermolecular interactions of polyphenols.[18] the formation process is controlled by the ionic strength. Optimal conditions to create MPNs and phenolic coatings were reported to be slightly alkaline with an ionic strength ≥0.5 M.1,19

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