In October 2013 I started my own group within the Laboratory of Organic Chemistry (at Wageningen University and Research), developing my research program at the interface of organic synthesis, supramolecular/dynamic-covalent chemistry and polymer science. Currently, my group’s research focusses on: 1) functional, antifouling coatings; and 2) dynamic, responsive polymers. In the former area controlled polymerisation methods are employed to grow well-defined antifouling coatings for (bio-)sensing applications. In the latter area, (macro)monomers are synthesised and subsequently self-assembled into polymer materials through reversible (dynamic-covalent and/or coordination) interactions. When assembled, their inherently dynamic nature renders these materials stimuli-responsive.
Dynamic, responsive polymers
The incorporation of dynamic covalent bonds in covalent polymers has enhanced polymer materials to become both robust and adaptive, leading to ‘smart’ materials that are, for example, self-healing or stimuli-responsive. In my group, we make use of dynamic covalent imine bonds for the construction of hydrolytically stable, multi-responsive coordination polymers. To this aim we combine imine bonds and tailored M–L bonds to obtain smart, dynamic covalent polymer materials that are responsive via their imine and M–L bonds, and through both bonds in concert.
As one of the key binding motifs we rely on a tridentate pincer ligand bearing a 2,6-diimino-pyridine moiety (see figure below), which is known to coordinate to various octahedral metal ions in a 2:1 fashion. The pincer, which consists of two dynamic covalent imine bonds (formed from 2,6-diformylpyridine and an amine) is capable of coordination to a metal ion in a 2:1 fashion. The overall metal-pincer complex, is highly dynamic: exchange is possible via both the imine bonds as well as the metal-ligand bonds. As such, this pincer can be considered as the dynamic covalent structural analogue of the classic terpyridine ligand.
Interested to read more on this type of research, check out our paper (Chem. Commun. 2016, 52, 9059) and our review (J. Pol. Sci., Part A: Polym. Chem. 2016, 54, 3551).
More recently, following the earlier work on dynamic, metal-stabilised imine-based polymer networks, and with the help of a NWO Vidi grant, we are now developing dynamic polymer materials that display a specific exchange mechanism, allowing them to behave like so-called vitrimer materials (read this review (Chem. Sci. 2016, 7, 30) to understand why these materials have exciting new properties).
Antifouling polymer brushes
False outcomes of diagnostic tests are a major concern in biomedical and biosensing applications. In order to make better and more reliable tests it is crucial to diminish background signals that arise from the non-specific binding of biomolecules onto sensor surfaces. To achieve this, repellent or so called antifouling layers can be incorporated between the sensor surface and its recognition elements (e.g. antibodies, sugars or peptides). The repellent layers we use are made of zwitterionic polymer brushes, and are grown from a variety of surfaces by surface-initiated Atom Transfer Radical Polymerisation.
Whilst exploring the variety of surfaces that these antifouling brushes can be grown from (which as of recently also includes microbead surfaces), we are also looking at approaches to install recognition elements onto, or into, these brushes to create so-called romantic surfaces: surfaces that only recognise their preferred partner, while repelling all other (bio)molecules.
Interested to read more on this type of research, check out the following papers: Langmuir 2019, 35, 1072 (review), ACS Appl. Mater. Interfaces 2017, 9, 38211 or Langmuir 2016, 32, 10199.
Please check out the Group Members section to get an overview of on-going projects in our lab.