Elisa Franzmann

Biomimetic PEG-catecholates for stabile antifouling coatings on metal surfaces: Applications on TiO2 and stainless steel

Trimeric catecholates have been designed for the stable immobilization of effector molecules on metal surfaces. The design of these catecholates followed a biomimetic approach and was inspired by natural multivalent metal binders, such as mussel adhesion proteins (MAPs) and siderophores. Three catecholates have been conjugated to central scaffolds based on adamantyl or trisalkylmethyl core structures. The resulting triscatecholates have been immobilized on TiO2 and stainless steel. In a proof of concept study we have demonstrated the high stability of the resulting nanolayers at neutral and slightly acidic pH. Furthermore, polyethylene glycol (PEG) conjugates of our triscatecholates have been synthesized and were immobilized on TiO2 and stainless steel. The PEG coated surfaces showed excellent antifouling properties upon exposure to human blood and bacteria as demonstrated by fluorescence microscopy, ellipsometry and a bacterial assay with Staphylococcus epidermidis. In addition, our PEG-triscatecholates showed no cytotoxicity against bone-marrow stem cells on TiO2.

A biomimetic principle for the chemical modification of metal surfaces: synthesis of tripodal catecholates as analogues of siderophores and mussel adhesion proteins.

By following a biomimetic design principle, tetravalent scaffolds based on an adamantyl and trisalkylmethyl core structure have been synthesized. These scaffolds have been coupled to three catecholamines, thus resembling the characteristic tripodal recognition motif of many natural metal binders, such as mussel adhesion proteins and siderophores, for example, enterobactin. Besides this tripodal recognition element, our scaffolds provide a fourth position for the conjugation of effector molecules. These effectors can be conjugated through biocompatible conjugation techniques to the scaffold and can be used to tailor the properties of different metal surfaces for a range of applications, for example, in implant engineering. Herein, we describe the synthesis of several tripodal metal binders and their immobilization on TiO(2) surfaces by using a simple dip-coating procedure. Furthermore, we demonstrate the conjugation of our surface binders to the dye eosin Y as an effector molecule by peptide coupling. The resulting surfaces have been analyzed by using ellipsometry, time-of-flight secondary ion mass spectrometry, IR spectroscopy, and contact-angle measurements to confirm the specific loading on TiO(2) films and nanoparticles with our trivalent surface binders. As a proof of concept, we have demonstrated the functionalization of TiO(2) nanoparticles with the eosin Y dye.

Synthesis of multivalent host and guest molecules for the construction of multithreaded diamide pseudorotaxanes

Summary A series of di-, tri- and tetravalent axles and wheels for the synthesis of pseudorotaxanes bearing the tetralactam macrocycle/diamide axle binding motif was prepared. Starting from iodinated monovalent precursors, Sonogashira cross-coupling reactions were utilized to couple the binding sites to appropriate spacer groups. Through this “Lego” or “toolbox” approach, the convergent synthesis of host and guests with a well-defined number of the binding sites is possible. In addition, the spatial arrangement of the binding sites can be controlled through the quite rigid connections between linker and binding sites. Although a quantitative assessment of binding strengths was not possible by NMR titration experiments, typical and significant shifts of the signals of the diamide moiety indicate qualitatively the formation of pseudorotaxanes from the axle and wheel precursors.