Photoswitchable supramolecular hydrogels
Numerous amphiphilic small molecules form hydrogels in contact with water. Responsive hydrogels are important for applications like controlled release of drugs, cell growth (implants), and adaptive materials. Light is non-invasive, precise in spatial and temporal manner, and as such is an ideal trigger for such systems.1
We synthesized a diketopiperazine derivative that contains an unnatural amioacid bearing an azobenzene photoswitch (PAP-DKP-Lys 1). It forms hydrogels in aqueous solutions. Addition of salt (NaCl) and acids improve mechanical properties of the gels. Some of them exhibit excellent self-healing properties. Irradiation with UV light causes gel-sol transition. DNA oligomers (polyacids) act as supramolecular cross-linkers that increase melting points of the gels.
The hydrogels can release previously encapsulated long dsDNA, or anticancer drug doxorubicin, upon irradiation at significantly higher rates than during passive diffusion in darkness.2 The structure and properties of these materials will be optimized for applications in living systems. We plan to replace azobenzene with more biocompatible photoswitches. We also investigate the scope and specificity of guest encapsulation in the gels.
Supramolecular hydrogel formed from PAP-DKP-Lys in water (left) becomes liquid upon UV light irradiation (right). The gel is reconstituted after irradiation with blue light.
Properties of gels formed by PAP-DKP-Lys in 50 mM aq. NaCl. Gel regeneration upon 30 sec. of 100% deformation (left), eSEM image of the hydrogel (right)
Intramolecular hydrophobic stacking and hydrogen bonding may stabilize fibers of the hydrogel composed of the trans-1 (left); upon photoisomerization to cis-1, the stabilization decreases, fibers are broken, the gel collapses (right).
Release of doxorubicin (a) or htDNA (b) from the hydrogel: 15 g/L 1. 2 g/L of DNA or doxorubicin in 50 mM aq. NaCl
 J. T. van Herpt, M. C. A. Stuart, W. R. Browne, B. L. Feringa Chem. Eur. J. 2104, 20, 3077-3083
 Z. Pianowski, J. Karcher, K. Schneider "Photoresponsive self-healing supramolecular hydrogels for light-induced release of DNA and doxorubicin" Chem. Commun., 2016, 52, 3143-3146.
Synthesis of novel biocompatible visible-light photoswitches
Efficient photomodulation of biological systems requires molecular switches operational under visible light and resistant on biodegradation (e.g. reduction with glutathion). Azobenzene photoswitches have excellent photophysical properties and exhibit high magnitude of changes (in terms of molecular size and polarity) upon photoisomerization. However, they may be sensitive for intracellular reducing environment, and are switched with UV light that is incompatible with living systems.3 We synthesize azobenzene derivatives that are resistant on physiological glutathione concentrations and can be bidirectionally switched with visible light. Therefore they may be successfully applied as components for photomodulation of biological systems. We prepare them as carboxylic acid derivatives – for functionalization of peptidonucleic acids – and as side chains of unnatural a-L-aminoacids for insertion into peptides or proteins, as well as into a new generation of the photoresponsive hydrogels described above.
We also work, in frame of the “Graduiertenkolleg 2039 – Molecular architectures for fluorescent cell imaging” - on the development of real-time fluorescent reporters of photoisomerization which can be used for detailed molecular investigations of the photomodulation process in biopolymers. http://www.grk2039.kit.edu/
 A.A. Beharry, G.A. Woolley, Chem. Soc. Rev., 2011, 40, 4422–4437; B. L. Feringa et al. Chem. Rev. 2013, 113, 6114-6178
Photoswitchable cell-permeable antisense agents
Antisense technology is a rapidly developing method of chemical biology and a promising tool for therapeutic applications. An antisense agent selectively binds to the target mRNA inside cells and prevents it from being translated into a functional protein. We want to synthesize cell-permeable photoswitchable antisense agents based on artificial oligonucleotides (GPNA) coupled to molecular photoswitches operational under visible light. Then we want to apply such agents to downregulate gene expression in vivo by light.
GPNA oligomers were successfully used as cell-penetrating antisense agents, efficiently downregulating expression of the EGFR receptor in the HNSCC and NSCLC cancer cell lines at the 3µM GPNA concentration.4 We want to modify GPNA oligomers with biocompatible photoswitches - either replacing one of the GPNA’s nucleobases or crosslinking its backbone. Photomerization of the photoswitch should cause sufficient conformational changes of the oligomer to destabilize its hybridization with a complementary RNA chain. And that will allow for switching the antisense effect on and off with light.
After initial in vitro validation, the method will be tested on mammalian cell cultures as well as on zebrafish embryos in order to obtain significant light-induced phenotype changes. Overall, we aim to create a practical technique for chemical optogenetics and dissection of complex biological systems (e.g. organism development) with high spatiotemporal precision.
 D. Ly, B. Armitage, et.al. ACS Chem. Biol. 2013, 8, 345-352.
Prebiotic systems chemistry
Self-replication of genetic information is the characteristic feature of life. All contemporary organisms share the common molecular framework based on DNA storage and enzymatic readout of the information. There are strong evidences that primordial genetic systems were based on RNA with catalytic abilities (“RNA world”). However, up to date no general mechanism for RNA autoreplication was proposed. We want to explore the capability of more robust and structurally simple genetic polymers for self-replication under abiotic conditions and their potential as a hypothetical component of the most primitive protocells. 
Our long-term goal is to create self-replicating evolutionary chemical systems that can become a component of an artificial cell and lead to synthetic life. Our research will also contribute to the discussion how likely life could independently develop outside Earth from simple molecules organized in chemical systems.
 J.M. Heemstrra, D.R. Liu J. Am. Chem. Soc. 2009, 131, 11347-49; M.R. Ghadiri et.al. Science 2009, 325, 73-77; Y. Brudno, M. E. Birnbaum, R. E. Kleiner, D. R. Liu Nature Chem. Biol. 2010, 6, 148-155