Surface-Confined Amorphous Films from Metal-Coordinated Simple Phenolic Ligands

Abstract

Coordination chemistry of natural polyphenols and transition metals allows rapid self-assembly of conformal coatings on diverse substrates. Herein, we report that this coordination-driven self-assembly process applies to simple phenolic molecules with monotopic or ditopic chelating sites (as opposed to macromolecular, multitopic polyphenols), leading to surface-confined amorphous films upon metal coordination. Films fabricated from gallic acid, pyrogallol, and pyrocatechol, which are the major monomeric building blocks of polyphenols, have been studied in detail. Pyrocatechol, with one vicinal diol group (i.e., bidentate), has been observed to be the limiting case for such assembly. This study expands the toolbox of available phenolic ligands for the formation of surface-confined amorphous films, which may find application in catalysis, energy, optoelectronics, and the biomedical sciences. ■ INTRODUCTIONModular control over the rational design of supramolecular architectures has been achieved in the last two decades by smart engineering of coordination-driven self-assembly processes. 1 Early prediction of the inherent preferences for directionality and binding affinity within the complementary building blocks of coordination complexes has paved the way for fabricating structures with extended networks of metal clusters bridged by compatible organic ligands. 2,3 Porous coordination polymers or metal−organic frameworks (MOFs) with distinct spatial and geometrical arrangements of the interconnecting motifs are examples of such organic−inorganic hybrid materials. 4−7 These crystalline materials with structurally encoded nano-and microporosities have potential application for gas storage, separations, and sensing. 8−13 On the other hand, surface-bound or freestanding amorphous thin films/coatings are another class of network materials of importance in several branches of science, 14−16 where polymeric compounds are commonly used structural components. Research has also focused on exploring novel strategies to incorporate inorganic moieties in polymeric films to obtain functional hybrid materials that exploit the synergistic effects of the organic and inorganic constituents. 17,18 In this context, processes utilizing self-assembly of coordination complexes are a promising strategy toward facile engineering of thin films with defined properties.Recently, we reported a facile assembly approach that exploits metal−polyphenol interactions, specifically between tannic acid (TA) and iron(III) (Fe III ) ions, to form thin films. 19 Our interest in these metal−polyphenol systems arises from the facile and versatile nature of the assembly process, which produces tunable, dynamic materials. Using TA as a ligand, we demonstrated the formation of capsules with engineered pHresponsive degradation, luminescence, and positron emission, by judicious choice of the incorporated metal, 20 as well as pHresponsive drug delivery vectors 21 and cytoprotective coatings. 22 Furthermore, we reported the assembly of Fe IIIpolyphenol capsules fro...

Stimuli‐Responsive Tannin–FeIII Hybrid Microcapsules Demonstrated by the Active Release of an Anti‐Tuberculosis Agent

“…[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] With respect to administration, especially to the human body,i deally such capsules should be fabricated based on ab iocompatibleb iodegradablep olymer consisting of an amphiphilic backbonet hat gives the possibility to bind equally efficiently to the hydrophobic core and cover it but also to have ah igh affinity to water. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] With respect to administration, especially to the human body,i deally such capsules should be fabricated based on ab iocompatibleb iodegradablep olymer consisting of an amphiphilic backbonet hat gives the possibility to bind equally efficiently to the hydrophobic core and cover it but also to have ah igh affinity to water.…”

Supramolecular design of coordination bonding architecture on zein nanoparticles for pH-responsive anticancer drug delivery

“…TA acted as organic ligand while metal ions were used as inorganic cross-linker [9,28]. The spontaneous complexation of metal ion with the TA catecholic unit was utilized to form films on zein NPs [29]. (without adjusting pH), the particle size of zein NPs was 96 nm with relatively small PDI (Fig.…”

Tailoring stimuli-responsive delivery system driven by metal–ligand coordination bonding

“…[35][36][37] The formation and cleavage of coordination bonds between TA and metal ions are pH dependent. 38 Herein, we engineered a kind of drug delivery system based on metal-TA films on zein/CMCS NPs, and the coated NPs exhibited controllable pH-dependent intracellular drug release (Scheme 1).…”

“…The metal-ligand films had controllable pH-dependent degradability, which led to an association of DOX release profile with the film degradation kinetics. [35][36][37]49 When the amount of Cu 2+ was increased, the onset of responsive pH dramatically reduced due to the high stability of the , which resulted in the fast release of DOX.…”