Jan O. Mueller

Controlled Cell Adhesion on Poly(dopamine) Interfaces Photopatterned with Non‐Fouling Brushes

Bioinspired poly(dopamine) (PDA) films are merged with antifouling poly(MeOEGMA) brushes utilizing a nitrile imine-mediated tetrazole-ene cycloaddition (NITEC)-based phototriggered surface encoding protocol. The antifouling brushes were photopatterned on PDA surfaces, leading cells to form confluent layers in the non-irradiated sections, while no adhesion occurred on the brushes resulting in a remarkably precise cell pattern. The presented strategy paves the way for the design of tailor-made patterned cell interfaces.

Adaptable Hetero Diels-Alder Networks for Fast Self-Healing under Mild Conditions

A novel adaptable network based on the reversible hetero Diels-Alder reaction of a cyanodithioester and cyclopentadiene is presented. Reversible between 50-120 °C, the adjustable and self-healing features of the network are evidenced via temperature dependent rheology experiments and repetitive tensile tests whereas the networks chemical structure is explored by temperature dependent (1) H MAS-NMR spectroscopy.

Light-Induced Modular Ligation of Conventional RAFT Polymers†

Making light work of RAFT conjugation: a non-activated RAFT agent at the end of RAFT polymers can readily be coupled with ortho-quinodimethanes (photoenols) in a photo-triggered Diels-Alder reaction under mild conditions without catalyst. The method is universal and opens the door for the conjugation of a large number of RAFT-prepared polymers with photoenol-functionalized (macro)molecules. (RAFT=reversible addition-fragmentation chain transfer.).

Photo‐Patterning of Non‐Fouling Polymers and Biomolecules on Paper

Functional cellulose substrates with tetrazole moieties are generated to serve as universal platforms for the spatio-temporal immobilization of synthetic ultra-low fouling polymer brushes and protein species via a nitrile imine-mediated tetrazole-ene cycloaddition (NITEC)-based protocol. Poly(carboxybetaine acrylamide) brushes are grafted from initiators photo-patterned by NITEC utilizing single electron transfer living radical polymerization. Streptavidin is photo-immobilized with remarkable efficiency, opening the possibility to generate new materials for biomedical and biosensing applications.

Efficient Photochemical Approaches for Spatially Resolved Surface Functionalization

Materials interfaces--with a gas, a liquid, or another solid--are highly important for advanced applications. Besides their topological design, controlling interactions at these interfaces is typically realized by tuning the chemical composition of the materials surface. In areas such as nanoscience or biology, it is, however, highly desirable to impart heterogeneously distributed properties. Photopatterning, more than micro- and nanoprinting methods, is often the method of choice for precise functionalization, especially in terms of versatility. Recently, a range of new or rediscovered photochemistry approaches have been applied to precision surface functionalization, with the common aim of increasing efficiency and resolution while concomitantly lowering the amount of required energy. A survey of such methods is presented in this Review, with a focus on those we have explored.

Sunlight-induced crosslinking of 1,2-polybutadienes: access to fluorescent polymer networks

The efficient sunlight-induced crosslinking of 1,2-polybutadienes to generate fluorescent patterns with spatial resolution is reported. The photochemical conjugation method employed is based on a nitrile imine-mediated tetrazole–ene cycloaddition (NITEC) reaction, which proceeds under UV-light irradiation (λmax = 312 nm) at ambient temperature in the absence of any catalyst. The NITEC reaction between 1-pentene and a newly designed di-linker, consisting of two photosensitive diaryl-substituted tetrazoles joined by a tetraethylene glycol spacer, was investigated in an initial study. Detailed characterization of a small molecule model study was performed by size exclusion chromatography (SEC), UV-vis and fluorescence spectroscopy as well as electrospray-ionization mass spectrometry (ESI-MS), which was also employed for monitoring the progress of the reaction (100% conversion in 20 min). Finally, two 1,2-polybutadienes of disparate molar masses were each photocrosslinked with the di-linker. The crosslinking reaction parameters, such as concentration, di-linker fraction and reaction time were optimized via SEC analysis and gravimetric determination of gel fractions. The applicability of the novel crosslinking technology for generating spatially controlled highly fluorescent gel patterns is demonstrated in a solvent-free reaction for 2 h under sunlight. In summary, the current study introduces an efficient light-triggered technology platform for crosslinking polymers carrying non-activated double bonds.

Fast and catalyst-free hetero-Diels-Alder chemistry for on demand cyclable bonding/debonding materials†

A new dithioester possessing a cyano Z-group (cyano-dithioester (CDTE)) has been synthesized via a 2-step, one-pot reaction. The cyano-substituted dithioester has been found to undergo fast reversible hetero-Diels–Alder (HDA) reactions at ambient temperature, without the need for a catalyst, as demonstrated by ESI-MS and UV-Vis experiments. To apply the bonding/debonding on demand system to materials science, a cyano-dithioester di-linker was synthesized and employed as a di-functional dienophile in a HDA-based polymerization reaction with a bis-cyclopentadiene polymer. The reversible bonding of the polymer systems were demonstrated by on-line UV-Vis spectroscopy, on-line NMR spectroscopy, and on-line high temperature DLS, as well as via GPC in situ trapping experiments and high-level ab initio molecular orbital calculations.

Visible‐Light‐Induced Click Chemistry

A rapid and catalyst-free cycloaddition system for visible-light-induced click chemistry is reported. A readily accessible photoreactive 2H-azirine moiety was designed to absorb light at wavelengths above 400 nm. Irradiation with low-energy light sources thus enables efficient small-molecule synthesis with a diverse range of multiple-bond-containing compounds. Moreover, in order to demonstrate the efficiency of the current approach, quantitative ligation of the photoactivatable chromophore with functional polymeric substrates was performed and full conversion with irradiation times of only 1 min at ambient conditions was achieved. The current report thus presents a highly efficient method for applications involving selective cycloaddition to electron-deficient multiple-bond-containing materials.

A Disulfide Intercalator Toolbox for the Site‐Directed Modification of Polypeptides

A disulfide intercalator toolbox was developed for site-specific attachment of a broad variety of functional groups to proteins or peptides under mild, physiological conditions. The peptide hormone somatostatin (SST) served as model compound for intercalation into the available disulfide functionalization schemes starting from the intercalator or the reactive SST precursor before or after bioconjugation. A tetrazole-SST derivative was obtained that undergoes photoinduced cycloaddition in mammalian cells, which was monitored by live-cell imaging.