Dr John Bacsa, Emory University

Testimonial from Emory University

Dr John Bacsa, Facilities Director of the Crystallography Lab at Emory University, USA, has been using the XtaLAB Synergy-S single crystal X-ray diffractometer since February 2017. Here, he talks about why he upgraded his system and his initial experiences and impressions of his newly-acquired X-ray diffractometer.

Dr. Bacsa discusses why a new diffractometer was required for the crystallography lab

The Emory University X-ray Crystallography Center housed two single crystal X-ray instruments that were routinely used by the investigators in the chemistry department. They were our primary instruments and were central to many of our past and current research activities. However, both instruments were over 16 years old and required frequent maintenance. Listed are some of the main reasons for the purchase of a new instrument

  • Support for the CCD detectors was no longer provided.
  • The Cu source instrument provided the larger anomalous signal for the determination of absolute configuration of chiral light atom molecules. The data collection times especially for the Cu source instrument and for small crystals was an issue.
  • The low intensity of the older sealed source was an issue.
  • We could not analyse small crystals.
  • Analysis of reactive, unstable intermediates was difficult.

As Director of the X-ray Center, concerns about future support and hardware failures and the need to keep us up-to-date with the current technology was the driving force behind the new purchase.

By comparing the data quality for the old and new instruments, Dr Bacsa highlights how these problems have been overcome or resolved with the new XtaLAB Synergy-S single crystal X-ray diffractometer.

We did get adequate data from standard and good quality crystals with our older instruments but looking back on the old data sets, I am surprised by the noise from the detector, the low intensities of the reflections and the poor data coverage. The new diffractometer has provided a different perspective on data quality and diffraction standards. We were limited to good quality crystals and I had to turn away many samples because the crystals were too small and/or poorly crystalline.

We get significantly better data with the new instrument. The speed at which we can collect data and solve a structure is impressive. Now, we use fast data collections (minutes long) to work out the connectivity of the compound. We regularly use the instrument to confirm reaction products. Considerably better data is obtained from smaller crystals. The boundary between samples that can be considered for a structural analysis has shifted considerably. We routinely determine structures of micro-crystalline and poorly crystalline samples with problems such as twinning, multi-domains and very large unit cell axes. We recently determined a structure with Z’=24. I do not think we would have detected this on the old system. High-resolution charge-density data (0.5 Å or better) with high redundancy is obtainable on most samples. Charge density data can be collected in under one-day.

Emory University have found that it is the combination of the individual components that make the XtaLAB-Synergy-S X-ray diffractometer so good.

Synergy is an apt name for this system. Specifically, the very large dynamic range and the sensitivity of the HyPix-6000HE detector allows high quality diffraction without overloads or long exposure times. The highly precise Kappa 4-circle goniometer enables efficient collection of complete data sets with short acquisition times. The dual micro-focus source with Mo and Cu sealed tubes running at 50 W of power output coupled with multilayer optics provides highly focused and intense X-ray radiation suitable for micro-crystals. The software is intelligently designed, flexible and is a key component of what makes the system so efficient. I enjoy being able to optimise and fine-tune the parameters such as I/sigma and the diffraction limits. We can normally tell a researcher almost immediately whether their sample is adequate and within a few minutes give them a preliminary structure.

One of the toughest crystal samples that has been collected on the new diffractometer at Emory University.

We have had several difficult samples but one example that stands out was a very reactive intermediate that would not crystallise (but was postulated to exist) and its structural characterisation was critically important for a researcher’s project. A microcrystalline precipitate formed in one of the vials. The microcrystals were visible under the highest magnification of our microscope. I selected a crystal less than 20 microns in diameter and a few microns thick (smaller than the loop) and got reasonably strong diffraction and a good crystal structure.

A message to anyone considering a new single crystal X-ray diffractometer

I underestimated the impact a new system would have on the workflow and our ability to analyse multiple samples. It has allowed us to remain competitive, and to be able to provide the necessary service support for research groups in the department.

I would recommend the system to anyone who is studying microcrystalline and sensitive structures. The system is easy to use, and this has made analysing samples really enjoyable!