Crystallography now and then: a talk with Professor Gautam Desiraju

Professor Gautam Desiraju needs no introduction. With a lifetime spent between crystals of all sizes and shapes, he has seen the many scientific methods succeed each other, flourish and being forgotten. Witnessing all metamorphoses a field of study can undertake in an accelerated knowledge transfer like our era’s, he is the perfect interlocutor for a talk on crystallography. What it was, what it amounts to and where it is heading, all was tackled on in an interesting talk with many questions answered and some more raised.

Crystal engineering: categories of technologies and their synergy

Who doesn’t like a good categorization? When we asked about his take on crystal engineering techniques, Professor Desiraju classified a very wide range of subjects into easier to grasp categories: the diffraction list, the spectroscopic branch and lastly, the eclectic computational branch. Moreover, he commented on of the complementarity of the three for a disruption-friendly environment in crystal engineering:

‘People are not scared anymore to use these techniques together. I believe that, in fact, one must combine them, because crystal interactions are both complex and subtle: very delicate tweaking can make big differences in the structures that can be designed.’

Crystallography: now and then

As a seasoned crystallographer, it was interesting to see Professor’s Desiraju outlook on crystallography in terms of past, present and future developments. Reminiscing the times of yore, with manual four-circle diffractometers and the escalation from papercuts to magnetic tapes, he comments that the shortening of time in the developments in the field which he witnessed make the evolution even more fascinating. He quickly retreats from this retrospection saying that maybe he is using a language which most crystallographers don’t understand anymore.

(So we move to the present and the future of crystallography.)

The challenges remain similar even though the lexicon has changed, he adds. One such ageless challenge is the size of the crystal for experiments, or the danger of samples not crystallizing.

‘One can have any kind of sophisticated design idea, put a molecule down on paper and try to start crystallizing it and simply not get crystals that are suitable for X-ray diffraction because they are not big enough and they are not big enough because for some reason the nucleation is too fast. There is no easy way to control the speed of nucleation.’

There are never enough crystal structures, he thinks. In the era of high throughput crystallography, with the million structures archived in the CSD, we still need more. And the ‘more’ comes from nano-crystals, twins, poorly-shaped crystals, impurities. These samples are not easy to study by X-ray diffraction, however. Electron diffraction can be a real breakthrough as it can tackle these nano-sized samples and restricting oneself to only X-rays for patent infringements, for example, could give way to blurry areas dictated by polymorph structures, fears Professor Desiraju.

What about not everybody recognizing right away the importance of electron diffraction?

‘When people are exposed to radically new ideas, it is better to also have strong opposition, because only if one can go through that strong opposition, then an idea will really be established, it will be then become a thing of the future.’

Thank you, Professor Desiraju, for this great talk. We believe that electron diffraction is indeed the thing of the future.