Interview with Christoph A. Schalley

Christoph A. Schalley

After chemistry studies at the University of Freiburg and the Technical University of Berlin, Christoph A. Schalley received his PhD with Prof. Helmut Schwarz at the Technical University Berlin, being trained in mass spectrometry and gas-phase chemistry. In particular, he worked on metal-catalyzed oxygen transfer reactions of peroxides and the generation of elusive reaction intermediates by neutralization-reionization mass spectrometry with water oxide being one of the highlights. His PhD thesis was followed by a postdoctorate supported by a fellowship from the Akademie der Naturforscher Leopoldina with Professor Julius Rebek, Jr. at the Scripps Research Institute in La Jolla, where he studied supramolecular capsules under environment-free conditions in the high vacuum of a mass spectrometer. Returning to Germany for his habilitation with Prof. Fritz Vögtle, Christoph Schalley started his independent career in the field of rotaxane chemistry. Meanwhile, his research covers not only rotaxanes and supramolecular gas-phase chemistry, but also the thermodynamic analysis of multivalent and cooperative binding, stimuli-responsive materials such as switchable gels and the generation of surfaces covered with mono- and multilayers of switchable rotaxanes. Christoph Schalley has co-authored more than 200 publications and edited eight books. For his work in the mass spectrometry and gas-phase chemistry of non-covalent complexes, he was awarded the Mattauch-Herzog Prize from the German Society for Mass Spectrometry in 2006. Since 2016, he has been a fellow of the Royal Society of Chemistry. Besides research, Christoph Schalley loves to teach and has been awarded with the Excellence-in-Teaching Award of the FU Berlin chemistry students twice in 2008 and 2014. Christoph Schalley has contributed to different fields in supramolecular chemistry. He was among those mass spectrometrists who popularized the investigation of non-covalent complexes under the environment-free conditions inside the high vacuum of a mass spectrometer. Beyond the analytical characterization, these studies offer unique insight into reaction mechanisms within supramolecular complexes, because the dynamic exchange processes that are often observed between the complexes in solution are completely suppressed and intramolecular reactivity is instead seen. Thus, the mobility of crown ethers along oligolysine peptides or on the periphery of POPAM dendrimers can be observed as well as cage contraction processes that do not occur in solution. In solution, the Schalley group investigated self-sorting phenomena and introduced the concept of integrative self-sorting, which allows the programming of larger assemblies that are formed from different building blocks. In such a case, kinetic path selection can often be observed, even though the final product eventually forms under thermodynamic control. Also, the analysis of multivalency effects and the importance of chelate cooperativity has been an important research topic in the Schalley group. More recently, the focus of the group has shifted more towards gels and supramolecular polymers on one side and surface chemistry on the other. Multistimuli-responsive gels have been prepared based on which a variety of logic gates can be implemented. Also, a very simple approach towards superhydrophobic and slippery, liquid-infused porous surfaces has been reported, which uses the deposition of supramolecular gels with perfluorinated side chains on glass surfaces. On gold, mono- and multilayers of chemically switchable rotaxanes show concerted switching between two clearly distinguishable states.

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What excites you most about supramolecular chemistry?

The virtually infinite variety of non-covalent aggregates with their particular kinetic and dynamic properties, which can be made stimuli-responsive and thus functional, with applications in a broad range of other disciplines from bio(in)organic chemistry to material sciences.

What are some of the greatest challenges you are facing now?

Supramolecular chemistry has come a long way from molecular recognition through templation, self-assembly, self-sorting and now is able to implement function. However, many of the functional systems that have been devised do not operate autonomously. Therefore, the new and emerging field of systems chemistry with its dissipative chemical systems inspires me a lot. Nevertheless, it is still a great challenge to design and properly realize such a system. Julius Rebek once wrote: “Some might say that supramolecular systems rescued physical organic chemistry. The discovery of crown ethers gave the field new recognition: molecular recognition” (Rebek, et al., JACS, 2001, 123, 11519). In a similar sense, I believe that systems chemistry is the future of supramolecular chemistry.

What inspired you to choose science and eventually become a chemist in the first place?

This is a tricky question as I was simply following my “gut instincts” and did not reason much about it…

What would you be doing if you weren't involved in science?

During my quantitative analysis practical course back in 1989, I was sufficiently frustrated to think about becoming a goldsmith or a harpsichord maker.

What advice would you give to someone interested in pursuing a career in your field?

Do the science you love and do it intensely as happiness comes when you get so involved that you forget about time.

What do you enjoy doing in your free time?

Biking, swimming, Richard Wagner's operas, architecture of the early 20^th century.

References

1. D. P. Weimann, H. D. F. Winkler, J. A. Falenski, B. Koksch and C. A. Schalley, Highly dynamic motion of crown ethers along oligolysine peptide chains, Nat. Chem., 2009, 1, 573–577.
2. T. Heinrich, C. H.-H. Traulsen, M. Holzweber, S. Richter, V. Kunz, S. K. Kastner, S. O. Krabbenborg, J. Huskens, W. E. S. Unger and C. A. Schalley, Coupled Molecular Switching Processes in Ordered Mono- and Multilayers of Stimuli-Responsive Rotaxanes on Gold Surfaces, J. Am. Chem. Soc., 2015, 137, 4382–4390.
3. L. Kaufmann, N. L. Traulsen, A. Springer, H. V. Schröder, T. Mäkelä, K. Rissanen and C. A. Schalley, Evaluation of Multivalency as an Organization Principle for the Efficient Synthesis of Doubly and Triply Threaded Amide Rotaxanes, Org. Chem. Front., 2014, 1, 521–531.
4. W. Jiang, K. Nowosinski, N. L. Löw, E. V. Dzyuba, F. Klautzsch, A. Schäfer, J. Huuskonen, K. Rissanen and C. A. Schalley, Chelate Cooperativity and Spacer Length Effects on the Assembly Thermodynamics and Kinetics of Divalent Pseudorotaxanes, J. Am. Chem. Soc., 2012, 134, 1860–1868.
5. W. Jiang and C. A. Schalley, Integrative Self-Sorting Is A Programming Language for High Level Self-Assembly, Proc. Natl. Acad. Sci. U. S. A., 2009, 106, 10425–10429.

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