Synthesis of tripodal catecholates and their immobilization on zinc oxide nanoparticles

Abstract

SummaryA common approach to generate tailored materials and nanoparticles (NPs) is the formation of molecular monolayers by chemisorption of bifunctional anchor molecules. This approach depends critically on the choice of a suitable anchor group. Recently, bifunctional catecholates, inspired by mussel-adhesive proteins (MAPs) and bacterial siderophores, have received considerable interest as anchor groups for biomedically relevant metal surfaces and nanoparticles. We report here the synthesis of new tripodal catecholates as multivalent anchor molecules for immobilization on metal surfaces and nanoparticles. The tripodal catecholates have been conjugated to various effector molecules such as PEG, a sulfobetaine and an adamantyl group. The potential of these conjugates has been demonstrated with the immobilization of tripodal catecholates on ZnO NPs. The results confirmed a high loading of tripodal PEG-catecholates on the particles and the formation of stable PEG layers in aqueous solution.

Surface Functionalization of Metal Oxide Semiconductors with Catechol Ligands for Enhancing Their Photoactivity

“…[ 66–68,89 ] TGA is another technique used to investigate the surface adsorption of catechol ligands onto metal oxides, particularly looking at the changes in the stability of metal oxide–catechol ligand complexes over a wide range of temperatures. [ 22,69,90,91 ] Surface adsorption is also verified using UV–vis as catechol surface functionalization generally shows redshifting and an increase in the absorbance peak. This results in improved photoabsorption in the visible range and increased photocurrent density.…”

“…These parameters provide a toolbox for predicting adsorption/desorption, co‐adsorption and ligand exchange behavior, which can be used to identify the optimal metal oxide and ligand concentration when preparing substrates for various applications. [ 22,90,91 ] DFT calculations can be used to quantitatively assess the binding affinity of catechol ligands and model their absorption on various metal oxide surfaces, and to evaluate changes of their optical absorption spectra and vibrational properties. [ 62,71,94 ] DFT studies show that the surface modification of metal oxides with catechol‐type ligands lowers the bandgap of metal oxides.…”

Surface Engineering of Nanostructured ZnO Surfaces

“…One of the limitations of catechol anchoring is represented by leaching of the grafted material consequently due to the reversible binding at neutral and slightly acidic pH, especially when in presence of physiological media. An attempt to overcome this limitation is reported by Klitsche et al In their work, three different multivalent cathecolates were immobilized on the surface of ZnO NPs and the corresponding binding properties to ZnO NPs analyzed. Monomeric PEG‐catecholate and tripodal were selected and their stability of the coatings and the particles in aqueous solution depending on the valency of the catecholate were investigated.…”

Contact-Biocide TiO2 Surfaces by Surface-Initiated Atom Transfer Radical Polymerization with Chemically Stable Phosphonate Initiators

“…Examples with alkoxysilanes, thiols, catechols, or phosphonates have been described . Phosphonate anchors are particularly attractive for SI-ATRP on TiO 2 , since they are known to form stable covalent bonds with TiO 2 − and a number of other metals and metal oxides. − The most widely used phosphonate initiator is 11-(2-bromo-2-methylpropanoyloxy)­undecyl phosphonic acid (BUPA). − Two other bromoisobutyrates have been described but are used less frequently for SI-ATRP on metals. − The effect of the initiator structure on SI-ATRP has not yet been investigated for phosphonate anchors. However, it is known that layer stability and loading density of phosphonates on metals and metal oxides depend on steric bulk and alkyl chain length. − One might therefore expect that the same would apply to the efficiency of SI-ATRP.…”