Featured Lab: X-ray Crystallography at the University of Zurich

A 10-minute read

What does it look like to work at the university that once hosted Wilhelm Röntgen, Max von Laue, and Peter Debye? Crystallography at its best! At the University of Zurich, Prof. Bernhard Spingler continues the long tradition by using X-ray crystallography not only for his own research, but also as a member of the X-ray crystallography service lab. As he solves structures of both small and not-so-small molecules, he is happy to know that his X-ray system has the optimal reliability and speed for measuring a high throughput of diverse samples. However, his interests do not stop there…

Even a quick glance at the University of Zurich gives a sense of X-ray crystallography’s rich tradition. Built on the shoulders of the giants of X-ray science, Wilhelm Röntgen, Max von Laue, and Peter Debye, the current research at the University’s Chemistry Department includes the eminent crystallographers Hans-Beat Bürgi, Anthony Linden, and Bernhard Spingler.

“Yes, I am a crystallographer“, Bernhard says with a smile, ”but, together with my group, I am also working on understanding processes that precede crystal structure determination.” Indeed, the group’s foci include the synthesis and characterization of biologically active compounds, as well as the crystal growth of small molecules and coordination compounds in general [1-4]. Although this broad research provides a number of crystals that could make any crystallographer happily busy, Bernhard does not shy away from other topics. He is also looking into large molecules, such as DNA, RNA, and proteins, and he is a member of a crystallography service team at the University.

X-ray service lab

The throughput of crystals in the service lab is high, but what is equally impressive is their variety. Crystals that come from Bernhard’s group and many other groups in the Chemistry Department include small and large molecules, strong and weak scatterers, and tiny and large crystals. With this in mind, the service crystallography lab had to find a reliable system, which can collect accurate data over a wide intensity distribution. The solution was found in a dual-source XtaLAB Synergy system equipped with a PILATUS3 200K, a durable detector with a large area and high efficiency for Cu- and Mo-radiation. “For four years now, the system has been running almost 24/7, and sometimes I joke that it is better than a synchrotron source because it has no shutdowns”, says Bernhard. “Throughout the years, the PILATUS3 has seen many samples from the University and beyond, and each project is special.”

Spingler’s group at the University of Zurich: the masks may cover their smiles, but the group is enthusiastic about growing and analyzing their single crystals.

Metal complex compounds: catalysts and phototoxic compounds

A good portion of the crystals that come to the service lab are metal coordination complexes from different groups. As these compounds find uses in various catalytic [5,6] and medical applications, Bernhard is interested in understanding their crystallization process, as well as their structure-property relationships. In one of his latest publications, he and his coworkers tackled the crystallization of Co(III) and Ru(II) bipyridine compounds [4], which are important for many light-to-energy applications. Using the nanocrystallization screening approach developed in the Spingler group [2,3], they generated several novel single-crystal structures with different anions. Data collection on one of the Co(II) complexes was carried out using the Cu-source, and this resulted in fluorescence. “The fluorescence signal was suppressed by adjusting the detector threshold to 7 keV”, comments Bernhard, “we enjoyed how nicely this useful feature is implemented in the CrysalisPro software!”

Also, as part of a study on photodynamic therapy, Bernhard is investigating compounds that are toxic to cancer cells upon light irradiation [7]. These phototoxic molecules are rather large and not trivial to crystallize, and their crystals often show disorder. “At this point, we are not producing an overwhelming number of phototoxic crystals”, Bernhard explains, “but we are happy our diffractometer allows us to increase the numbers without compromising other research topics.”

Big and bigger organic molecules

Not surprisingly, Bernhard is also curious about big molecules and their interactions with metals and metal complexes. He investigated interactions of DNA [8] and RNA [9, 10] with cations, tackled challenging vitamin B12 crystals [11], and determined the structure of nicotinamide riboside [12]. Crystallographic data on RNA was obtained at the X06Da macromolecular crystallography beamline at the Swiss Light Source, while the B12 derivatives were measured at the University of Basel. At that time, that University of Basel installed a STOE STADI diffractometer with a Metal Jet source and a PILATUS3 R 300K detector. Now, Bernhard and his group are excited to tackle large molecules using their own PILATUS3 at the University of Zurich.

Phototoxic compound [trans-PtCl(NH3)2]4-5,10,15,20-tetra(4'-pyridyl)-zinc(II)porphyrin tetraphenylborate (DMF)7 [7]. Non-coordinated anions and DMF molecules not coordinated to the zinc metal center were omitted for clarity. The crystals were grown by the under-oil method with an extensive anion screen as described in [3]. This data for that structure was collected on a PILATUS3 R 200 K DECTRIS detector.

Future work

“Crystallography is an integral part of our research, and we are sure that we will keep our diffractometer busy with crystals of small and big molecules”, reveals Bernhard. Nonetheless, he and the group are looking into electron diffraction to extend their research towards micro- and nanocrystals. “As a researcher, I am excited to see how new instrumentation and electron detection technologies increase the quality of electron diffraction data. As a service crystallographer, I am happy to see that this technique is ready to provide reliable and high throughput measurements that can complement single-crystal X-ray diffraction.”

We wish Bernhard Spingler and his group a good continuation of their research projects, as well as smooth operation of the X-ray service crystallography lab.

Want to know more about DECTRIS detectors that are used in laboratory diffractometers for research and in service labs?

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References

1. Spingler, B. et al. (2012) CrystEngComm. 14(3), 751-757.
2. Nievergelt, P.P., et al. (2018) Chem. Sci. 9(15), 3716-3722.
3. Babor, M. et al. (2019) IUCrJ 6(1), 145-151.
4. Alvarez, R. et al. (2020) Dalton Trans. 49(28), 9632-9640.
5. Hernández-Valdés, D. et al. (2020) Dalton Trans. 49(16), 5250-5256.
6. Hernández-Valdés, D. et al. (2020) Helv. Chim. Acta 103(10), e200147.
7. Rubbiani, R. et al. (2020) Chem. Commun. 56(92), 14373-14376.
8. Rohner, M. et al. (2016) Inorg. Chem. 55(12), 6130-6140.
9. Phongtongpasuk, S. et al. (2013) Angew. Chem. Int. Ed. 52(44), 11513-11516.
10. Schaffer, M. et al. (2016) Int. J. Mol. Sci. 17(7), 988.
11. Prieto, L. et al. (2016) Org. Lett. 18(20) 5292–5295.
12. Alvarez, R. et al. (2019) Cryst. Growth Des. 19(7), 4019-4028.