The IUCr Newsletter is the web magazine of the International Union of Crystallography. Since 1993, the IUCr Newsletter has been published quarterly and distributed to over 13,000 crystallographers worldwide. In August 2018, it was transformed into a dynamic digital platform with a fresh new look. Its aim remains to bring together the crystallographic community.
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William L. Duax Patricia Potter Jane Griffin The IUCr Newsletter is distributed electronically to 13,000 crystallographers and other interested individuals in 102 countries. Articles from the Newsletter are also available on this web site by following the links on the left-hand side. Feature articles, meeting announcements and reports, information on research or other items of potential interest to crystallographers may be submitted to the editor at any time. Items will be selected for publication on the basis of suitability, content, style, timeliness and appeal. Please send contributions to: newsletter@iucr.org Matters pertaining to advertisements should also be sent to the above address. Email address changes or corrections and requests to be added to the mailing list should be accomplished through the Subscribe and Unsubscribe hyperlinks above. Reuse permissions • The original article in which the material appeared is cited. • Copyright permission is indicated by the wording "Reproduced with permission of the International Union of Crystallography Newsletter". In electronic form, this acknowledgement must be visible at the same time as the reused materials, and must be hyperlinked to the IUCr Newsletter (http://www.iucr.org/news/newsletter). Please be sure to include the following information: • The title, author(s) and page extent of the article you wish to republish, or, in the case where you do not wish to reproduce the whole article, details of the section(s) to be reproduced. • The volume/issue number and year of publication in which the article appeared, and the page numbers of the article. • Details of the publication in which you wish to reprint the Newsletter material. • If the material is being edited or amended in any way, a copy of the final material as it will appear in your publication. • Contact details for yourself, including a postal address. |
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The IUCr Newsletter (ISSN 1067-0696; coden IUC-NEB) is published quarterly (4x) by the International Union of Crystallography (IUCr Executive Secretary e-mail execsec@iucr.org). Members receive the IUCr Newsletter by virtue of country membership in the IUCr. Periodical postage rates paid at Buffalo, NY and additional mailing offices. POSTMASTER: Please send changes of address to IUCr Newsletter Editorial Office, c/o Hauptmann-Woodward Medical Research Institute, 700 Ellicott St. Buffalo, NY 14203 USA.
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![[Fig. 1]](https://www.iucr.org/__data/assets/image/0009/154386/Slide4.PNG)
The IUCr is pleased to invite nominations for the 2023 Struchkov Prize. Professor Yuri T. Struchkov (1926–1995) was an outstanding Russian crystallographer who made substantial contributions to the structural chemistry of organic and organometallic compounds. To commemorate Professor Struchkov's achievements, his friends and former colleagues established the Struchkov Prize in 1997. Between 1997 and 2020, the Prize was awarded annually to a young (<35 years) scientist from the Former Soviet Union (FSU) for the best research work in the field of X-ray crystallography.
In 2020, the Struchkov Prize Association asked the IUCr to administer the Prize to ensure its longevity. From now on, the Prize will be bestowed by the IUCr every triennium at the IUCr Congress and General Assembly beginning in Melbourne in 2023. The Association has endowed a Prize Fund. Any interest earned on the Fund, along with any donations received during the triennium, will be split equally between the winners. The principal of the Fund can never be used to supplement the Prize. The IUCr will select a committee that will consider nominations and determine the winners.
The Struchkov Prize will be awarded to up to three young scientists (under 35 years of age at the time of the submission deadline) at each Congress for outstanding achievements in small-molecule X-ray diffraction methods application in the fields of chemistry, crystal chemistry or materials science.
Applicants for the 2023 competition may be nominated or self-nominate. The following information should be submitted:
By submitting an application, the applicants agree to provide the submitted content to the organising committee and members of the jury. Applications should be submitted electronically to the IUCr Chief Executive Officer at ceo@iucr.org. The closing date for nominations is 30 September 2022.
Crystal structures are not static; they contain a wealth of information about dynamics and reactivity of molecules and extended solid materials. On the one hand, dynamic properties are related to the atomic and lattice vibrations in crystals, so that an accurate description of both atomic displacement parameters and diffuse scattering are important for crystallographic experiments. Disorder in crystals may be also related to dynamic behaviour, and the description of dynamic behaviour renders the determination of thermodynamic properties of crystals possible. On the other hand, series of related crystal structures can be understood as snapshots along a pseudo-reaction pathway, which relates ‘static’ crystallography to chemical reactivity.
These aspects of structural science have been major themes in Hans-Beat Bürgi’s scientific career spanning nearly 60 years. Structure correlation, disorder, and the dynamics of atoms and molecules in crystals remain important but sometimes still underrated fields of structural chemistry today. For those reasons, we have taken the opportunity to highlight these topics in this thematic special issue dedicated to Hans-Beat Bürgi on the occasion of his 80th birthday this year.
Hans-Beat Bürgi’s university education in the Chemistry Department of the Federal Institute of Technology (ETH) Zürich culminated in the completion of his PhD research in 1969 under the supervision of Jack Dunitz. After a two-year postdoctoral stint with Lawrence (Larry) Bartell at the University of Michigan, focusing on structure determination in the gas phase by electron diffraction, Hans-Beat returned to single-crystal X-ray diffraction and to the laboratory of inorganic chemistry at the ETH for his habilitation work leading a small independent research group. In this period between 1971 and 1979, many of the ground-breaking studies that determined Hans-Beat’s career were undertaken, such as the development of the structure correlation idea (Bürgi, 1973) of which the highly cited concept of the Bürgi–Dunitz angle of nucleophilic attack at carbonyls is part (Bürgi et al., 1974). The cover illustration of this special issue [see above] shows Hans-Beat at the blackboard in Zürich in 1974, explaining the concept to a guest researcher from Japan.
His substantive position for nearly 30 years was Professor and Director of the Laboratory of Chemical and Mineralogical Crystallography at the University of Bern (Fig. 1). During this time, Hans-Beat established himself as one of the leading international authorities of X-ray crystallography. Many of his achievements are described and reflected in this special issue, and he has described them in substantial detail in a recent essay in the Israel Journal of Chemistry (Bürgi, 2017), so we have not attempted to list or summarize them here. In his post-retirement roles as an Emeritus Professor in Bern and a permanent academic guest at the University of Zürich, Hans-Beat continues as an active researcher who does not miss a single day in the office.
![[Fig. 1]](https://www.iucr.org/__data/assets/image/0004/154966/me6183fig1.png)
Throughout his distinguished career, Hans-Beat has held visiting appointments at Princeton University, the Australian National University in Canberra, Technion in Haifa, Caltech in Pasadena, Tokyo Institute of Technology, University of California Berkeley and San Diego, and the University of Western Australia. With the end of the Covid pandemic, he plans to revive some of these collaborations during his annual trips around the world from winter in Switzerland to summer in Australia, then on to New Zealand, California, and back to Switzerland just when winter has passed in the northern hemisphere.
In preparation for this special issue, we had naturally contacted Jack Dunitz who, in May last year, astonished Mark by a phone call at his home in Perth, and Simon in his office in Bern. Jack was genuinely disappointed that he could not contribute, as with macular degeneration he was no longer able to write. But he did very vividly paint for us a picture of Hans-Beat as a young scholar. Jack said that Hans-Beat had always stood out from others for his insatiable interest in (chemical) science and discussions around it. If necessary, he could stand his ground with much older and more established colleagues in heated discussions from early on in his career. Hans-Beat’s perseverance and accuracy when finishing a study for publication was also something that Jack remembered. There were supposedly hour-long discussions between the two of them around the formulation of a single paragraph in a manuscript draft. In the end, the quality of the published work speaks for itself. In this context, it is worth reading the obituary that Hans-Beat wrote for Jack Dunitz, published in the previous issue of Acta Crystallographica B (Bürgi, 2022).
Hans-Beat has not lost any of the characteristics that Jack Dunitz attributed to the young scholar. He is well known in the crystallographic community as the critical mind who always has a question at the end of a scientific talk, and who enjoys to passionately discuss. Along the same lines, Hans-Beat’s dedication to teaching and mentoring young crystallographers and his excellent didactic skills have been widely recognized and appreciated for some time. Among his many other achievements, Hans-Beat has been director of an Erice School of Crystallography in 1991 and, with Tony Linden, he continues to be an organizer and director of the Zürich School of Crystallography that he co-founded upon retirement in 2007 (Fig. 2). It will see its 10th edition this year, and the 2024 School is already in the planning.
![[Fig. 2]](https://www.iucr.org/__data/assets/image/0005/154967/me6183fig2.png)
We also compiled a list of Hans-Beat’s scientific colleagues and collaborators, and in early 2021 invited them to contribute in the form of personal reminiscences, research papers or review articles. Given the disruption caused by the global pandemic, we were delighted that most invitees were both keen and willing to contribute to this festschrift volume. We were especially pleased to receive personal contributions from Dieter Schwarzenbach, Roald Hoffmann, Jean-Marie Lehn and Hans-Beat himself, and these are included as Opinion pieces at the beginning of this special issue. Two Topical Reviews follow that are fundamentally different in content and reflect the considerable breadth of Hans-Beat’s interests: a review of bone hierarchical structure by Henrik Birkedal et al., as well as a review of X-ray constrained wavefunction fitting by Dylan Jayatilaka et al. The research articles in this special issue are dedicated to numerous aspects of dynamics in crystals, disorder, structure correlation and even quantum crystallography and, on the latter field, Hans-Beat has contributed an additional critical commentary. Finally, we are indebted to the many scientific referees whose willingness to support this special issue was remarkable, reflecting Hans-Beat’s standing among, and respect from, the international community of crystallographers and structural chemists.
Bürgi, H. B. (1973). Inorg. Chem. 12, 2321–2325.
Bürgi, H.-B. (2017). Isr. J. Chem. 57, 109–116.
Bürgi, H.-B. (2022). Acta Cryst. B78, 270–273.
Bürgi, H. B., Dunitz, J. M., Lehn, J. M. & Wipff, G. (1974). Tetrahedron, 30, 1563–1572.
This article was originally published in Acta Cryst. (2022). B78, 281–282.
Although recent decades have seen significant progress in the opportunities for carrying out crystal structure determination directly from powder X-ray diffraction (XRD) data (McCusker, 1991; Harris et al., 2001; David & Shankland, 2008; Etter & Dinnebier, 2014; Černý, 2017), this task is still considerably less routine than structure determination from single-crystal XRD data. In some cases, the structure determination process fails at the first stage, namely unit-cell determination (often referred to as ‘indexing’ the powder XRD data), such that the process cannot progress to the subsequent structure solution and structure refinement stages. For reasons highlighted below, unit-cell determination from powder XRD data can encounter challenges under certain circumstances, which may represent an insurmountable hurdle in the structure determination process. Specific challenges arise in cases of poor-quality powder XRD data (for example, when severe peak broadening arises due to poor crystallinity of the sample) and/or poor-quality samples (for example, containing an unknown impurity crystalline phase).
In light of the challenges that can arise in unit-cell determination, the report of a strategy by Schmidt and co-workers (Habermehl et al., 2022) that essentially circumvents the indexing step in structure determination from powder XRD data will be welcomed with interest by practitioners in the field. However, to place this development in context, it is relevant first to explain briefly the methodology for indexing powder XRD data, and the reasons that challenges may be encountered in this stage of the structure determination process.
Unit-cell determination involves analysis of the ‘positions’ of Bragg reflections in the powder XRD data, where ‘position’ refers to the diffraction angle 2θ or the corresponding d-spacing. The aim is to find a set of unit-cell parameters (a, b, c, α, β, γ), together with the corresponding set of Miller indices (h, k, l) for each Bragg reflection, that successfully account for the positions of all peaks in the powder XRD data. Typically, the positions of about 20 peaks are used in the indexing process, measured from the low-2θ region of the experimental powder XRD data, where the extent of peak overlap is less than in the high-2θ region. It is important to note that the aim of the indexing stage is to establish a good initial approximation to the correct unit cell, which is then improved in subsequent profile-fitting calculations [typically carried out using the algorithms of Pawley (1981) or Le Bail (1988)] to generate a more accurate set of unit-cell parameters for use in subsequent structure solution and refinement calculations.
In the early days, when powder XRD data were measured on photographic film and data analysis relied on mathematical insight rather than computational power, the challenges associated with unit-cell determination were already well recognized (Henry et al., 1961), and a number of approaches were pioneered for indexing such data (Hesse, 1948; Vand, 1948; Lipson, 1949; Ito, 1949; de Wolff, 1957). Subsequently, the emergence of computer technology stimulated the development of a wide range of new strategies for unit-cell determination from powder XRD data (Taupin, 1968; Visser, 1969; Kohlbeck & Hörl, 1976; Werner et al., 1985; Boultif & Louër, 1991; Paszkowicz, 1996; Kariuki et al., 1999; Coelho, 2003; Neumann, 2003; Habershon et al., 2004; Le Bail, 2004; Altomare et al., 2009; Oishi-Tomiyasu, 2014; Louër & Boultif, 2014), many of which form the basis of indexing programs that are widely used today.
With this large array of computational approaches at our disposal, unit-cell determination from powder XRD data often proceeds straightforwardly and successfully. However, a number of factors can limit the chances of success in specific circumstances. Two particularly serious situations are: (i) severe peak overlap in the powder XRD data (which may limit the ability to extract accurate values of peak positions, as required for indexing calculations, and can even obscure the existence of certain peaks that may be crucial for successful indexing), and (ii) the presence of a crystalline impurity phase in the powder sample (such that the set of peak positions used for attempted unit-cell determination actually arise from two different unit cells).
Problems of severe peak overlap arise in the case of samples that give broad peaks in the powder XRD pattern, for example due to poor crystallinity and/or particle size effects. In such cases, it may be challenging to extract a sufficient number of reliable peak positions from the powder XRD data to allow successful indexing. Furthermore, even for samples of good crystallinity, significant peak overlap can still arise in cases with large unit cells and/or low symmetry due to a high density of peaks in the powder XRD pattern, even though the individual peaks are relatively narrow. This situation often arises for organic molecular materials. In such cases, measuring the powder XRD data using a synchrotron radiation source may help to alleviate the extent of peak overlap by minimizing the instrumental contribution to peak widths, and hence may be conducive to successful indexing.
To assess whether failure to index a powder XRD pattern is due to the presence of an impurity crystalline phase in the powder sample, independent evidence may be established by other experimental techniques (particularly solid-state NMR) or simply by checking whether the powder XRD pattern contains peaks due to plausible impurity phases of known crystal structure (such as known polymorphs of the material of interest). In favourable cases, the impurity phase may be identified as a material of known structure, in which case the peaks due to the impurity phase can be readily excluded from the indexing calculation, allowing successful unit-cell determination using only the peaks for the phase of interest (for example: Al Rahal et al., 2019). In some cases, the existence of two crystalline phases in a powder sample may be identified by observing that the powder XRD data contain two sets of peaks with significantly different peak widths (for example: Dinnebier et al., 1997).
Of course, when attempts to index a powder XRD pattern prove to be problematic, other experimental techniques may be exploited to determine the unit-cell parameters for the material of interest, such as electron diffraction (for example: Gorelik et al., 2009; Smalley et al., 2022) or measurement of XRD data for magnetically oriented micro-crystalline arrays (Kimura & Kimura, 2018). Another approach to generate possible unit cells independently of the powder XRD data is to take advantage of crystal structure prediction algorithms (Price, 2014; Woodley et al., 2020), which generate a set of energetically feasible crystal structures for the molecule of interest; in principle, one of the crystal structures may be found to give an acceptable match to an unindexed experimental powder XRD pattern (for example: Paulus et al., 2007).
Although the approaches discussed above provide a wide range of opportunities to overcome problems encountered in indexing powder XRD data, the development of structure determination protocols that effectively circumvent the indexing stage may be seen as an attractive alternative. The strategy reported by Schmidt and co-workers (Habermehl et al., 2022), entitled ‘Structure determination from unindexed powder data from scratch by a global optimization approach using pattern comparison based on cross-correlation functions’, achieves this objective by combining unit-cell determination and structure solution within a single process, rather than handling them as sequential stages on the structure determination pathway. The methodology, which is embodied within the program FIDEL-GO, requires only an experimental powder XRD pattern and knowledge of the molecular structure as input information. The strategy starts from a set of trial crystal structures generated by random selection of both the unit-cell parameters and the arrangement of molecules within the asymmetric unit, with the space groups of the trial structures selected from a set of ‘common’ space groups. The strategy then applies a multi-step procedure for global optimization, with the ultimate aim of generating structural models that give an acceptable quality of fit to the experimental powder XRD data by optimization of both the unit-cell parameters and the set of structural variables that define the atomic positions within the asymmetric unit. In common with standard practice in direct-space structure solution of molecular materials from powder XRD data (Harris et al., 2001; David & Shankland, 2008), the structural models used in FIDEL-GO are typically based on the assumption of standard bond lengths and bond angles (although one example discussed by Schmidt and co-workers includes relaxation of certain bond lengths), and the set of structural variables comprises, for each crystallographically independent molecule, the position of the molecule in the unit cell, the orientation of the molecule with respect to the unit-cell axes and a set of variable torsion angles that define the molecular conformation.
Importantly, a critical aspect underlying the FIDEL-GO approach is the selection of an appropriate method to assess the quality of agreement between the powder XRD pattern calculated for each trial structural model and the experimental powder XRD pattern, as the similarity measure used for this assessment must be able to give a meaningful indication of the quality of agreement even when the unit cell for the trial structural model deviates significantly from the correct unit cell. This task is achieved using a similarity measure based on a weighted cross-correlation function, specifically the generalized similarity measure S12 defined previously by de Gelder et al. (2001).
Following the optimization process, promising structural models generated by FIDEL-GO are subjected to an automated Rietveld fitting procedure to provide a more reliable assessment of the quality of fit to the experimental powder XRD data. The authors recommend that this stage is then followed by manual Rietveld refinement calculations as the final step of the process, to allow a robust ranking of the best candidate structures to be determined.
The authors note that their approach has a tendency to generate several different structures that give a similar quality of fit to the experimental powder XRD data. Clearly, under such circumstances, it is essential to further scrutinize the validity of the candidate structures using information from other computational (for example, DFT-D) and experimental (for example, solid-state NMR) techniques, in order to provide robust and conclusive evidence that the correct structure has actually been assigned on the basis of the final Rietveld refinement calculations. The application of methods for structure determination from PDF data (Billinge, 2019) for the same material may also be valuable in this regard (for example: Schlesinger et al., 2021).
It is important to note that the concept of carrying out unit-cell determination and structure solution from powder XRD data synchronously within the same protocol has been reported in previous studies (Hofmann & Kuleshova, 2006; de Gelder et al., 2008; Padgett et al., 2007; Rapallo, 2009; Guguta et al., 2019), which are based on a variety of different strategies for carrying out optimization of the fit to the experimental powder XRD data, in some cases incorporating information from calculations of the energetic properties of trial crystal structures. The workflow of the FIDEL-GO algorithm also includes the opportunity to carry out DFT-D calculations, particularly in the context of validation of promising candidate structures in the final stages of the structure determination process.
The successful application of the FIDEL-GO strategy is demonstrated by structure determination of four materials from powder XRD data of poor quality, described by the authors as ‘un-indexable’, typically containing only a relatively small number broad peaks. In comparison to current capabilities in the application of direct-space structure solution using high-quality (‘indexable’) powder XRD data, the selected materials represent structural problems of relatively low complexity, defined by a small number of structural variables (two of the four examples are rigid molecules, for which no variable torsion angles are required to define the intramolecular geometry, while the other two examples involve only a few variables to define the intramolecular geometry). Nevertheless, the successful structure determinations reported by Schmidt and co-workers clearly represent promising progress in demonstrating the feasibility of the FIDEL-GO strategy, and the success is particularly notable given the poor quality of the experimental powder XRD data used in some of their applications. Certainly, the results of future applications of FIDEL-GO to tackle structural problems of greater complexity, defined by a higher number of structural variables, will be eagerly awaited.
By demonstrating the prospect of achieving successful crystal structure determination from poor-quality powder XRD data, the FIDEL-GO strategy certainly offers a promising opportunity that may prove to be particularly beneficial when challenges are encountered in applying the conventional approaches for indexing powder XRD data.
Al Rahal, O., Hughes, C. E., Williams, P. A., Logsdail, A. J., Diskin–Posner, Y. & Harris, K. D. M. (2019). Angew. Chem. Intl Ed. 58, 18788–18792.
Billinge, S. J. L. (2019). Philos. Trans. R. Soc. A, 377, 20180413.
Boultif, A. & Louër, D. (1991). J. Appl. Cryst. 24, 987–993.
Černý, R. (2017). Crystals, 7, 142–151.
Coelho, A. A. (2003). J. Appl. Cryst. 36, 86–95.
David, W. I. F. & Shankland, K. (2008). Acta Cryst. A64, 52–64.
Dinnebier, R. E., Olbrich, F., van Smaalen, S. & Stephens, P. W. (1997). Acta Cryst. B53, 153–158.
Etter, M. & Dinnebier, R. E. (2014). Z. Anorg. Allg. Chem. 640, 3015–3028.
Gelder, R. de, Guguta, C. & Smits, J. M. M. (2008). Acta Cryst. A64, C149.
Gelder, R. de, Wehrens, R. & Hageman, J. A. (2001). J. Comput. Chem. 22, 273–289.
Gorelik, T., Schmidt, M. U., Brüning, J., Beko, S. & Kolb, U. (2009). Cryst. Growth Des. 9, 3898–3903.
Guguta, C., Smits, J. M. M. & de Gelder, R. (2019). ChemRxiv. Cambridge: Cambridge Open Engage. https://chemrxiv.org/engage/chemrxiv/article-details/60c740a6bdbb892770a381cf.
Habermehl, S., Schlesinger, C. & Schmidt, M. U. (2022). Acta Cryst. B78, 195–213.
Habershon, S., Cheung, E. Y., Harris, K. D. M. & Johnston, R. L. (2004). J. Phys. Chem. A, 108, 711–716.
Harris, K. D. M., Tremayne, M. & Kariuki, B. M. (2001). Angew. Chem. Int. Ed. 40, 1626–1651.
Henry, N. F. M., Lipson, H. & Wooster, W. A. (1961). The Interpretation of X-ray Diffraction Photographs, pp. 177–188 and pp. 242–244. London: MacMillan.
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Smalley, C. J. H., Hoskyns, H. E., Hughes, C. E., Johnstone, D. N., Willhammar, T., Young, M. T., Pickard, C. J., Logsdail, A. J., Midgley, P. A. & Harris, K. D. M. (2022). Chem. Sci. 13, 5277–5288.
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As reported by Dr Hanna Dabkowska in her Letter from the President in this issue of the IUCr Newsletter, the IUCr has named Dr Alex Stanley as its first Chief Executive Officer. Dr Alex Stanley will succeed Dr Alex Ashcroft, IUCr Executive Secretary, who retires at the end of August 2022.
Alex Stanley holds a PhD in Chemical Crystallography from the University of Bristol, UK, and has a good understanding of many scientific fields related to structural science. She brings experience not only from a society level, having acted as the Bursaries Co-ordinator and Secretary for the British Crystallographic Association and as a UK delegate at the IUCr General Assembly, but also from an industrial level, having worked for Agilent Technologies, Oxford Diffraction and Rigaku. Her skill base is broad as she has experience in managing people, projects and budgets, in product marketing, building a brand identity, and in governance at committee and corporate levels.
The long handover period will help in the transfer of this complex leadership role and will mean that both Alexes will attend the IUCr Executive and Finance Committee meetings in Versailles, France, in August, overlapping with ECM33.
Dr Dabkowska commented: "I am thrilled that Dr Stanley is joining our ranks. I sincerely believe that this international organisation will achieve new heights under her leadership. We are a strong team of people very proud of the job they are doing. We are happy to have Alex in control and I trust she will guide us towards many new future achievements.”
Dr Stanley commented: "I am excited to join the IUCr whose core values of community, integrity and passion for promoting high-quality structural science are so very evident. I look forward to building on the strong foundations, put in place by Alex Ashcroft and his predecessor Mike Dacombe, to support this well-regarded organisation."
Dr Ashcroft commented: "I am delighted that Alex has been appointed, and that the IUCr is in safe hands."
Dr Stanley can be contacted at ceo@iucr.org.
It is fair to state that in chemical research the least expected results can be the most interesting. In this issue of IUCrJ, Butler et al. (2022) report the discovery of a new molecular solid – a two-component crystal of water and 2,2,6,6-tetramethylpiperidine (TMP) – formed as a by-product during the course of a study on a different subject, namely the deprotonation of ferrocene derivatives using TMP as base. The new substance, which has a simple composition of TMP·2H2O and is stable in a vacuum manifold but is degraded when exposed to air at room temperature, has a number of features that would not have been easy to predict.
The most prominent structural feature is the formation of what Butler et al. describe as a water pipe. The structure, which was analyzed by single-crystal X-ray and neutron diffraction at 100 K and by neutron diffraction at 10 K, has a central channel with TMP molecules at its periphery and with water molecules forming an inner lining of the channel walls. (Such a lining can be called a bushing in mechanical jargon, but that term has not often been applied to water-based channel linings in molecular crystals.)
The overall layout of the structure, as viewed in a projection along the channel axis, can be described as a rhombic distortion of a square-prismatic proto-structure. The water aggregate has a distorted cubic motif, which is stacked along the channel axis. The presence of latent symmetry, in which the aggregate structure has more or at least different symmetry than do the individual components, dovetails with the fact that the new solid forms only for a very specific proportion of the components – the H2O:TMP molar ratio must be 2:1. When this odd couple of two quite different molecules do form the solid, though, they apparently do so readily, yielding centimetres-long rod-shaped crystals.
Further interest lies in the fact that both of the pure components are liquids at room temperature. This ‘liquid–liquid co-crystallization’ has been observed previously, but to my knowledge, it does not abound (Peloquin et al., 2020).
I might refer to the new solid as a co-crystal to reflect the observation that H2O is a full structural partner and is not merely present as a dispensable solvate. However, that would risk venturing into the definition of a co-crystal, a complex subject that has been treated more fully by others (Bond, 2007; Parkin et al., 2008; Aitipamula et al., 2012).
Beyond the existence of the channel lined by water is the suggestive fact that there is disorder among the sites of the water hydrogen atoms. This is where the use of single-crystal neutron diffraction is critical, since with this technique even half-occupied proton sites can be characterized accurately. The TMP2H2O structure has segments of hydrogen-bonded chains, which may be identified as proton wire fragments. A proton wire was the key structural element in a previous discovery by Capelli et al. (2013), in which it was proved by a deuterium substitution experiment that the protons along a disordered hydrogen-bonded chain of water molecules were mobile in crystals of a manganese coordination polymer.
The concept of a proton wire merits a brief description, because such a construct may exist in more crystals than those in which it has been explicitly identified as such. As described by Nagle & Morowitz (1978), a simple proton wire consists of a chain of hydrogen bonds along which proton transport can occur. The Grotthuss mechanism, a two-step "bucket-brigade" model, is invoked to explain the proton movement along the chain (Ädelroth, 2006; Cukierman, 2006).
The example reported by Capelli et al. (2013) has an unbounded proton wire and is an ideal example for discussion, since, as mentioned, that system was shown by experiment to transport protons. In that study, a neutron structure analysis revealed disorder between two stages of a putative Grotthuss proton transport mechanism. The disorder is shown in Fig. 1, which is based on the atomic coordinates from the neutron diffraction analysis by Capelli et al. (2013). The H(A) and H(B) sites are half-occupied and H(AB) are fully occupied. In Fig. 1(a) congener (A) is present, indicated by solid blue bonds and solid blue H atoms. The arrows indicate the concerted rotations that move protons from the H(A) to the H(B) sites in one stage of the Grotthuss mechanism. In Fig. 1(b), in which the H(B) sites are now occupied (solid blue bonds and atoms), the arrows represent proton hopping to nearby empty H(A) sites. This stage of the mechanism restores the original configuration shown in Fig. 1(a), except that each of the H(A) protons has moved to the next oxygen carrier atom along the chain.
The structured, extended water aggregate in TMP·2H2O, supported by its walled TMP enclosure, may be capable of at least short-range proton transport. In addition to its structural features and possible dynamics, there is a lesson in the fact that the TMP·2H2O crystal forms at all. This new and interesting solid was not the target of the research that produced it. It seems that nature has not exhausted its store of surprises, and we cannot know when our next unexpected observation will turn out to be an opening to a new avenue of exploration.
The author thanks Dr Milagros Tomás for incisive observations on the subject matter of this commentary.
The following funding is acknowledged: Ministerio de Ciencia e Innovación (grant No. PGC2018-093451-B-I00); European Union Regional Development Fund (award No. FEDER); Diputación General de Aragón (grant No. E11_20R).
Ädelroth, P. (2006). Biochim. Biophys. Acta, 1757, 867–870.
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Bond, A. D. (2007). CrystEngComm, 9, 833–834.
Capelli, S. C., Falvello, L. R., Forcén-Vázquez, E., McIntyre, G. J., Palacio, F., Sanz, S. & Tomás, M. (2013). Angew. Chem. 125, 13705–13709.
Cukierman, S. (2006). Biochim. Biophys. Acta, 1757, 876–885.
Nagle, J. F. & Morowitz, H. J. (1978). Proc. Natl Acad. Sci. USA, 75, 298–302.
Parkin, A., Gilmore, C. J. & Wilson, C. C. (2008). Z. Kristallogr. Cryst. Mater. 223, 430.
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This article was originally published in IUCrJ (2022). 9, 331–332.
Between December 2020 and July 2021, several spectacular developments in the field of protein-structure prediction changed structural biology profoundly, and they are expected to have an impact on much of modern (molecular) biology, medicine, biochemistry and biotechnology. The unprecedented accuracy of blind protein-structure predictions produced by DeepMind’s AlphaFold2 was revealed at the CASP 14 meeting in December 2020. In July 2021, this was followed by publication of the method and release of the code (Jumper et al., 2021). Simultaneously, a prediction method from the Baker lab that achieved similar accuracy was published (Baek et al., 2021). A week later, an additional publication described proteome-scale application of protein-structure prediction using AlphaFold2. This coincided with the launch of a new resource in which DeepMind and EMBL–EBI collaborate to make hundreds of thousands (and, eventually, hundreds of millions) of high-quality predicted protein structures openly available: the AlphaFold Protein Structure Database, or AlphaFold DB (Tunyasuvunakool et al., 2021; Varadi et al., 2022). These developments stunned not only the protein-structure prediction community, but most of the structural biology, bioinformatics, and machine-learning communities and beyond. It was truly an 'annus mirabilis'.
Much has been said and written about these developments in the scientific, technical and popular press (not to mention on social media) and the journal Nature Methods selected protein-structure prediction as its Method of the Year (Editorial, 2022). The potential impact of the developments has also been the subject of much prognostication and speculation. When AlphaFold DB was first announced, a group of senior EMBL structural biologists released a white paper discussing its possible impact (https://www.embl.org/news/science/alphafold-potential-impacts/). At the time of writing (late May 2022), using the term ‘alphafold’ to search the literature at Europe PMC (https://europepmc.org/search?query=alphafold), there are over 700 published research papers, over 150 unpublished preprints and, somewhat astonishingly, almost 300 review papers.
The structural community was impressively quick to embrace the new resources (both the software and the database) and a flurry of preprints appeared in bioRxiv within weeks, both analysing the holdings of the database (e.g. correlating the estimated reliability of models and the location of intrinsically disordered regions in proteins) and putting the software through its paces (e.g. various ‘hacks’ to make AlphaFold2 predict structures of multimeric complexes). Experimental structural biologists were also quick to react and within days of AlphaFold DB being announced and the AlphaFold code being released, there were many reports of structures (X-ray and cryo-EM mostly) that had previously resisted solution but that suddenly could be cracked using one or more (parts of) AlphaFold (DB) models. Methods and software developers were also quick to adapt their procedures and programs to make use of the astonishing new opportunities offered by high-quality protein-structure predictions. Over time, scientists outside the structural field are expected to embrace and discover the power of the new methods and the fact that soon a structure model will be available (or easily obtainable) for just about any protein sequence, be it natural or designed. Moreover, developments in the structure-prediction field will continue, e.g. concerning structure prediction for macromolecular and ligand complexes, RNA, post-translational modifications, and the impact of point mutations. The full scientific impact will take many years to be realized, and by then the new tools (methods and models) will be textbook material for undergraduate curricula.
While this is all fantastic news for bioscience, medicine and biotechnology, there are also concerns, not least in the field of structural biology, regarding the impact of these developments on funding and careers. We understand that when the announcement of AlphaFold DB was made via the CCP4 mailing list, there was a crystallography course ongoing, and the news made some of the students on the course question their study or career choices. We wouldn’t be surprised if, upon first hearing the announcements, more than a few structural biologists went through several of the five stages of grief (denial, anger, bargaining, depression and acceptance) and have asked themselves questions such as: ‘Is there even a need for experimental structure determination anymore?’, ‘Is there a future career in structural biology for me?’, ‘Will it be possible to get tenure in this field?’, ‘Will funding agencies now think that structure determination is not necessary and stop funding my projects/methods development efforts?’, ‘Will expensive infrastructure (synchrotrons, microscopes, spectrometers) still get funded?’.
It is almost unavoidable that there will be changes in terms of funding and career opportunities. However, as the adage (attributed to Einstein) goes: ‘In the midst of every crisis, lies great opportunity.’ Perhaps this time of profound change in our field is merely a transition to a new golden era for structural biology. For one thing, structure prediction still has limitations and is anyway not a panacea; also, predictions will need validation. More importantly, there will be entirely new opportunities leading to a ‘new normal’ in structural biology which will, in turn, support a new normal in biology. This means that there will continue to be a need for experimental structure determination (and the requisite people and infrastructure). However, it is likely that structures can generally be determined much more quickly than before and hence that we can focus more on the real objective of structural biology: to understand or influence function, mechanism, activity, binding interactions, etc. using structural information (as well as other biophysical and computational methods). Moreover, in the wider field of biology, medicine, biotechnology, agriculture etc., there will be a huge need for scientists (and teachers) who know and understand structures, who can assess which parts of a structure, be it experimental or predicted, are likely to be reliable enough to (help) answer the biological question that is posed, who can assess which prior biological data about function etc. can be explained in light of a structure, who can compare multiple related structures and draw sensible conclusions, and who can help design follow-up experiments based on the insights gained from structures. In summary, we are optimistic that, far from witnessing the end of structural biology, we are part of an exciting revolution in biology where structure will play a much more prominent role than in the past, at least on a par with the role that protein sequences are playing today.
Baek, M., DiMaio, F., Anishchenko, I., Dauparas, J., Ovchinnikov, S., Lee, G. R., Wang, J., Cong, Q., Kinch, L. N., Schaeffer, R. D., Milla´n, C., Park, H., Adams, C., Glassman, C. R., DeGiovanni, A., Pereira, J. H., Rodrigues, A. V., van Dijk, A. A., Ebrecht, A. C., Opperman, D. J., Sagmeister, T., Buhlheller, C., Pavkov-Keller, T., Rathinaswamy, M. K., Dalwadi, U., Yip, C. K., Burke, J. E., Garcia, K. C., Grishin, N. V., Adams, P. D., Read, R. J. & Baker, D. (2021). Science, 373, 871–876.
Editorial (2022). Nat. Methods, 19, 1.
Jumper, J., Evans, R., Pritzel, A., Green, T., Figurnov, M., Ronneberger, O., Tunyasuvunakool, K., Bates, R., Žídek, A., Potapenko, A., Bridgland, A., Meyer, C., Kohl, S. A. A., Ballard, A. J., Cowie, A., Romera-Paredes, B., Nikolov, S., Jain, R., Adler, J., Back, T., Petersen, S., Reiman, D., Clancy, E., Zielinski, M., Steinegger, M., Pacholska, M., Berghammer, T., Bodenstein, S., Silver, D., Vinyals, O., Senior, A. W., Kavukcuoglu, K., Kohli, P. & Hassabis, D. (2021). Nature, 596, 583–589.
Tunyasuvunakool, K., Adler, J., Wu, Z., Green, T., Zielinski, M., Žídek, A., Bridgland, A., Cowie, A., Meyer, C., Laydon, A., Velankar, S., Kleywegt, G. J., Bateman, A., Evans, R., Pritzel, A., Figurnov, M., Ronneberger, O., Bates, R., Kohl, S. A. A., Potapenko, A., Ballard, A. J., Romera-Paredes, B., Nikolov, S., Jain, R., Clancy, E., Reiman, D., Petersen, S., Senior, A. W., Kavukcuoglu, K., Birney, E., Kohli, P., Jumper, J. & Hassabis, D. (2021). Nature, 596, 590–596.
Varadi, M., Anyango, S., Deshpande, M., Nair, S., Natassia, C., Yordanova, G., Yuan, D., Stroe, O., Wood, G., Laydon, A., Žídek, A., Green, T., Tunyasuvunakool, K., Petersen, S., Jumper, J., Clancy, E., Green, R., Vora, A., Lutfi, M., Figurnov, M., Cowie, A., Hobbs, N., Kohli, P., Kleywegt, G., Birney, E., Hassabis, D. & Velankar, S. (2022). Nucleic Acids Res. 50, D439–D444.
This article, which is based on a presentation by the same authors at the 2022 CCP4 Study Weekend, was originally published in IUCrJ (2022). 9, 399–400.
Science, like art, requires creativity,
but creativity without love is impossible.
– G. V. Wulff
In 2023, it will be 160 years since the birth of Georg (Yuri) Viktorovich Wulff (Вульф in Russian, also known as Vulf and Wulff) (Fig. 1). He was born on 22 June 1863 to a large family in the city of Chernigov (according to other sources, in the city of Nizhyn, Chernigov province) of the Russian Empire (now Ukraine). His mother, Lydia Egorovna, was a daughter of a famous teacher, E. V. Gudim, who came from the nobility of the Poltava province. His father, a teacher of literature, Viktor Konstantinovich Vulf, served as the director of the Chernigov, later of Poltava and 6th Warsaw, Gymnasiums. Georg spent his childhood and youth in Warsaw, where in 1880 he graduated from the 6th Warsaw Gymnasium. From childhood, he showed interest in exact disciplines.
After graduating from the gymnasium, Georg entered the Natural Department of the Faculty of Physics and Mathematics of the Imperial Warsaw University (Poland was then part of the Russian Empire). From the second year, he began to engage in scientific work under the guidance of a mineralogist and crystallographer, Professor A. E. Lagorio, and physicists Professor N. G. Egorov and Professor P. A. Zilov. Professor Egorov took the mineralogist student into the world of physics, showing that there are properties of crystals that are reflected in their external forms. The main focus of Wulff's studies was on physics and crystallography, which was then considered a branch of mineralogy. Being just a third-year student, he was awarded the gold medal of the Faculty of Physics and Mathematics for his work “Experimental Study of the Electrical Properties of Quartz”, the topic of which was proposed by Professor Zilov. In this experimental work, this talented student managed to show that the electrification of quartz crystals is associated with a piezoelectric effect. The work was published in the periodical Варшавские университетские известия (Warsaw University News) in 1886. In his fourth year, Wulff was already assisting in lectures on physics by Professor Zilov, who taught physics at the highest methodological level.
After graduating from the University in 1885, on the recommendation of Professor Lagorio, Wulff remained at the University at the Department of Mineralogy to prepare for professorship and, at the same time, was enrolled as an assistant at the Department of Physics. With Professor Lagorio, he studied the heat capacity of minerals, and under the guidance of Professor Zilov, he performed several studies on the dependence of the optical properties of crystals on their crystallographic characteristics. The results of the study of crystals that rotate the plane of polarization were summarized in his 1888 paper "On the Theory of Rotatory Polarization". The study of the physical, primarily optical, properties of crystals led him to create his own direction in science, which was later called "crystal physics". In many cases, experimental studies by G. V. Wulff can rightfully be considered to be pioneering. His contribution to the development of solid-state physics can be assessed from the book by Academician V. D. Kuznetsov, Solid State Physics (1937).
After the master’s exam in 1888, Wulff did his best to be sent to St. Petersburg University, where he worked for six months in the Mineralogical Cabinet. At that time, an outstanding, now world-famous Russian crystallographer E. S. Fedorov, author of the monograph “The Foundation of the Teachings of Figures”, in which he laid the foundations of theoretical crystallography and derived all possible 230 space groups of symmetry of crystals, also worked there. Wulff highly appreciated E. S. Fedorov's achievements and later, with Professor P. von Groth, contributed to the popularization and publication of his works. For example, Wulff published abstracts of Fedorov’s main works in German in Zeitschrift für Krystallographie und Mineralogie, of which von Groth was the founder and an editor, trying to establish the priority of the Russian scientist in the field of theoretical crystallography. Communication with Fedorov influenced his formation as a crystallographer. There he also met V. I. Vernadsky, whom he later found to be a like-minded person, in all respects, not just in science and teaching, but also in political and public issues.
At the beginning of 1889, Wulff was sent abroad, first to Munich, to von Groth, a famous crystallographer and representative of the German crystallographic school, in whose laboratory he laid the foundations of his master's thesis. In addition to working in von Groth's laboratory, Wulff listened to his lectures on crystal physics and attended Professor Zonke's seminars in physics at the Polytechnic School. Studying crystals of salts, he concluded that it is possible to reveal the internal structure of a crystal by correlating its external form and symmetry with physical, primarily optical, properties. In crystals of beryllium sulfate, he discovered a composition of two pseudosymmetric plates, and in a double salt, lithium potassium sulfate, he revealed the rotation of the polarization plane.
Then, in 1890 and 1891, Georg Viktorovich worked in Paris at the laboratory of the famous French physicist Professor A. Cornu, where he studied physical methods for studying crystals, in particular, the elasticity of solid bodies, primarily the properties of glass. Wulff discovered that the Poisson ratio of these materials was not 0.25, as was found by Cornu, but 0.23, which means that glass does not have the properties of an isotropic body. While they tried to find out the cause, V. Foygt also obtained the value of 0.23, which meant that Wulff could not publish his numerous experimental data. Wulf published the results of his work in Paris later, only in 1893–1894, in Warsaw University News. In Paris, Wulff married Vera Vasilyevna Yakunchikova (she took his family name), and together they lived a long life.
Returning to Warsaw, Georg Wulff defended his master's thesis “The Properties of Some Pseudosymmetric Crystals in Connection with the Theory of the Crystalline Structure of the Substance” (1892). Wulff was one of the first crystallographers who, when trying to solve the problem of the structure of crystals, began to use their physical properties, such as optical activity and piezoelectric and elastic properties. Having received the title of Privatdozent of Warsaw University (1893), Wulff began to give lectures on mineralogy and crystallography.
At the same time, Wulff turned to the experimental side of crystallography. For two years, he was engaged in experiments on the growth and dissolution of crystals. He measured relative growth rates of various crystalline faces, building up layers of one crystal upon the layers of another, composed of an isomorphic substance but of different color. Wulff also studied the effect of concentration flows on the morphology of growing crystals. To eliminate irregularities in the growth of crystals, he invented a rotating crystallizer, used thermostats with temperature controllers, and developed a method for obtaining crystals of regular habit. Critical and interesting studies of the growth rate and dissolution of the faces of crystals were carried out by Wulff on the example of Mohr's salt. He showed that the rate of dissolution of various faces of crystals of this salt is almost the same, while the growth rates of these faces significantly differ from each other.
Studying the processes of crystal growth, Wulff modified Curie's principle of the minimum of the surface energy of crystals growing from saturated solutions in equilibrium conditions. It was later called the "Gibbs–Curie–Wulff principle" (or "Wulff Theorem"), according to which the growth rate of the faces of the crystal is proportional to specific surface energies of these faces. The essence of the Wulff theorem can be determined by the following expression: n1:n2:n3:... = k1:k2:k3:.., where ni are the lengths of perpendiculars (Wulff's vectors), directed through the faces from the central point taken inside the crystal (Wulff's point), and ki is the specific surface energy of the face (capillary constants of faces). Thus, normals to the faces are proportional to the capillary constant and express the growth rate of the crystal's faces under constant concentration conditions. At each moment of such stationary growth, the surface energy of the crystal has the lowest value corresponding to the volume that the crystal has at this moment. That is, during the growth of the crystal, provided that constant concentrations are maintained, its faces move away from the growth point of the crystal (Wulff's point) with speeds equal to the Wulff's vectors, which are proportional to the capillary constants.
Wulff published the results of his two-year-long studies in 1895 in Warsaw University News in the work “On the Issue of Growth and Dissolution of Crystalline Faces”, which he presented at the Physics and Mathematics Faculty as a dissertation for the degree of Doctor of Mineralogy and Geognosy. In this work, the author monitored the correlation of external forms and optical properties of crystals with their internal structure and with crystallization conditions. Wulff's modern biographers call it one of the most significant works on crystallography performed at the University of Warsaw. However, at the University itself, this non-traditional pioneer work was not appreciated and was rejected under the pretext of its insufficient volume. Georg Viktorovich was able to defend a dissertation only a year later at the Imperial Novorossiya University in Odessa (1896). After his article appeared in Zeitschrift für Kristallographie und Mineralogie, the theorem on the proportionality of the growth rate of capillary constants of faces was recognized and received the name of the author.
With the advent of two-circle or theodolite goniometers (E. S. Fedorov, 1889), it became easier to measure the angles between crystal faces. E. S. Fedorov was the first to use stereographic projections to present the results of crystal measurements. However, Wulff alone succeeded in developing in 1902 a simple graphical method for processing the results using a stereographic grid. His method turned out to be very convenient; it quickly gained popularity and spread among crystallographers world-wide, and was named after the author – "Wulff net" (Fig. 2).
![[Fig. 2]](https://www.iucr.org/__data/assets/image/0004/154984/Fig2.jpg)
He also proposed the "Wulff ruler" designed by him. Using the Wulff net, you can graphically calculate the symbols of all crystal faces, as well as the crystal constants – axial angles. The Wulff net is still used in crystallography today. In 1904, Wulff published his Guide to Crystallography, which is in many ways a synthesis of his work in this area. In geometric crystallography, one of the most important works of Wulff was devoted to the analysis of errors in measuring crystals with a theodolite goniometer.
An interesting feature of teaching at the University of Warsaw was that teachers could declare optional courses that were related to their personal interests. Wulff took advantage of this and, in the 1896/1897 academic year, declared an optional course on the symmetry of crystals for second- and third-year students. In this course, he presented crystallographic symmetry in an original way, using successive reflection only in planes (textbooks by G. V. Wulff Fundamentals of Crystallography, 1923, and Crystals, Their Formation, Type and Structure, 1926) (Fig. 3).
![[Fig. 3]](https://www.iucr.org/__data/assets/image/0005/154985/Fig-3.JPG)
Wulff considered planes of symmetry to be the main "independent elements of symmetry", as reflection cannot be reproduced by either rotation or inversion taken separately. He deduced all 32 types of symmetry of crystals, which today we call crystallographic point groups, and came up with his own nomenclature and ways of designating it (Fig. 4).
![[Fig. 4]](https://www.iucr.org/__data/assets/image/0006/154986/Fig-4.jpg)
Wulff wrote about the wholeness of the concept of symmetry, that symmetry is a consequence of reflection in one or more mirror planes acting either separately, or in pairs (axes are obtained), or in threes (inversion center is obtained). Contemporaries did not accept Wulff's proposals and continued to use the familiar symbols of Schoenflies, and later the international symbols (Hermann–Maugin).
In 1897, Wulff accepted an offer from the Ministry of Education and left to work as an extraordinary professor at the Department of Mineralogy and Crystallography at the Imperial Kazan University. However, after A. E. Lagorio was appointed as director of the Warsaw Polytechnic Institute, Wulff returned to Warsaw in 1899 and held the position of ordinary professor at the Department of Mineralogy.
The revolutionary situation in Russia in 1905 was accompanied by student unrest. In particular, students demanded that teaching at Warsaw University should not be conducted in Russian, but in Polish, the native language of most of the students. Wulff considered these requirements fair and publicly supported the students, which caused the discontent of colleagues and the leadership of the faculty. In connection with student unrest in 1906, the classes were suspended and resumed only in 1908. In this situation, Wulff worked only until he had gained 20 years of experience, which gave him the right to resign the professorship. He decided to finally leave Warsaw University and go to Geneva, where his family then lived. Saying goodbye to students of Warsaw University, Wulff called on them to be selflessly devoted to science: “... The desire for truth will only be fruitful when you are imbued with love for the truth. Science, like art, requires creativity, and creativity without love is impossible. ... Love the truth and be, above all, humans, in the noble sense of the word ... ".
In 1907, Wulff moved to Moscow at the invitation of V. I. Vernadsky. In the same year, he was approved as a Privatdozent of the Department of Mineralogy of the Physics and Mathematics Faculty of Moscow University. Since 1908, Wulff also read the crystallography course at Moscow University and at the A.L. Shanyavsky Moscow City People's University. In 1909 and 1910, at Moscow University, Wulff lectured on crystallography and crystal optics, using his crystallographic net in practical classes. Thanks to the support of Vernadsky, who was the head of the Department, Wulff got the opportunity to found his crystallographic laboratory, which was equipped, at his own expense, in the premises of the Mineralogical Institute. A. V. Shubnikov, who later became an outstanding Russian crystallographer, worked there as a student. At Moscow University, Wulff closely communicated with the famous physicist P. N. Lebedev, and actively participated in the work of colloquia at his physical laboratory, on the basis of which the Moscow Physical Society was organized in 1911. Lebedev was elected the first chairman of the Society (Wulff was elected the chairman of the Society in 1921). At the same time, he taught a course in crystallography at Moscow University and at the A.L. Shanyavsky Moscow City People's University.
At the University, Wulff continued to pursue studies in geometrical crystallography and started a new topic – the study of liquid crystals, about which he made reports at the general meeting of the Russian Physicochemical Society (1908), and at the XII Congress of Russian Natural Scientists and Physicians, in the Physics section (1910).
However, shortly after a strike at Moscow University in 1911, Wulff, because of his independent nature and beliefs, left the University together with a group of progressive professors in protest against the reactionary policy of the Minister of Education, L. A. Casso. Moscow University lost its best professors, including P. N. Lebedev, V. I. Vernadsky, N. A. Umov, N. D. Zelinsky and K. A. Timiryazev.
Wulff went to work at the A.L. Shanyavsky Moscow City People's University, in which he had already given a course of crystallography lectures starting from its founding in 1908. Wulff’s crystallographic laboratory was also transferred there, for which he himself purchased equipment and materials, spending all his university earnings. There, Wulff carried out his experimental work. At the same time he gave lectures on crystallography and mineralogy at Moscow Higher Women's Courses.
In 2022, it will have been 110 years since the fundamental discovery of the diffraction of X-rays by crystals made by Max von Laue, a Privatdozent at the University of Munich, and his colleagues (article in Nature in 1912, the 1914 Nobel Prize). Wulff immediately appreciated the value of this discovery. He founded the first X-ray laboratory in Russia and actively took up the study and deciphering of X-ray diffraction by crystals. Based on the experiments of Laue and independently from W. L. Bragg, Wulff theoretically deduced the condition for the interference of X-rays reflected from crystals, known in Russian-speaking literature as the “Wulff–Bragg” or “Bragg-Wulff formula”. In the same 1913, a month earlier, W. L. Bragg published the well-known equation called "Bragg's law":
2dsinθ = nλ
(where d is the interplanar spacing, θ is the glancing angle (or Bragg corner), n is the diffraction order and λ the wavelength).
Studying the history of the development of X-ray diffraction analysis, the Russian historian of chemistry, Doctor of Science A. M. Smolegovsky, noted that the question of the priority of deriving the Bragg–Wulff equation remains unclear. It is known that both scientists made their reports on this topic as early as the end of 1912, and published their work at the beginning of 1913. Brief information on the content of Bragg's report was published in Nature in December 1912. In an article dedicated to the 75th anniversary of the discovery of X-ray diffraction, an outstanding scientist in the field of solid-state physics and X-ray diffraction analysis, G. S. Zhdanov, wrote that the formula that was empirically found by Bragg and theoretically established by Wulff can rightly be considered the “Wulff–Bragg formula”.
Professor A. K. Boldyrev (a disciple of E. S. Fedorov) wrote in the textbook on his lectures Fundamentals of Crystallography (1926) and in the book Crystallography (1934) that “this is an empirical law, derived even earlier by Professor G.V. Wulff on the basis of Laue's experimental data." The theoretical substantiation of this law was derived in different ways – Bragg substantiated it more simply and elegantly than others. Smolegovsky writes that Bragg's student H. Lipson later opposed the use of the expression "Wulff–Bragg Law" in scientific and educational literature. Wulff himself, in the book Crystals, Their Formation, Form and Structure (1926, second edition), gives his original derivation of the formula with different notation and also notes that "this equation, fundamental to the whole phenomenon, was independently derived by W. L. Bragg and the author of this book". Considering that Bragg and Wulff were working independently in this field at the same time, it is fair to say that both scientists deserve to have this law named after them – the "Bragg–Wulff Law". The English version of Wikipedia formulated it as follows: "Bragg's law”, “Wulff–Bragg's condition” or “Laue–Bragg interference”.
In 1913–1914, father and son Bragg, inspired by Laue's discovery, improved the mathematical apparatus and technique (ionization spectrometer) and devised a standard procedure for determining the structures of crystals. They determined the structures of a number of crystalline substances, such as NaCl, KCl, KBr, ZnS (sphalerite) and diamond. The work was extremely successful and already in 1915 the first monograph by W. H. Bragg and W. L. Bragg was published, in which they described the structures of 33 substances. In the same year, father and son Bragg received the Nobel Prize, but it was awarded only in 1919, after the end of World War I. Lawrence Bragg is still the youngest Nobel laureate to receive this prestigious award for natural science research.
Apparently, because of this success, the name "Bragg's law" is widely used in the world scientific literature for the well-known expression, which allows one to determine the crystal structure from the diffraction pattern, while the name of Professor Wulff remained in the shadows. When translating the Braggs' book X-rays and the Structure of Crystals (1916), Wulff highly appreciated the work of his English colleagues. He wrote that, despite the simultaneous derivation of this law by the author of the book and the translator, "this coincidence in no way detracts from the significance of the results obtained by the Braggs, and it is in these results that the interest of the research of these scientists lies."
This is how X-ray diffraction analysis – the main reliable method for determining crystal structures – was born. In 2023, the famous Bragg–Wulff formula, which marked the beginning of a new scientific discipline, X-ray crystallography, will be 110 years old. The accumulation and analysis of data on the structure of crystals led to the creation of the first tables of atomic radii (W. L. Bragg, W. Goldschmidt, L. Pauling), which laid the foundations of a new science – crystal chemistry. The significance of these pioneering works can hardly be overestimated, since subsequently, extensive structural databases were created, which are necessary for the fruitful and efficient work of scientists from various fields.
Professor A. K. Boldyrev wrote about the significance of Laue's discovery, which also applies to the Bragg–Wulff law: "From now on, more than ever before, Crystallography is most intimately connected with Physics and Chemistry, and the further development of this science goes before our eyes under the sign of this connection. And we clearly realize that only in this connection lies the guarantee of its future achievements". Paying tribute to the work of Professor Wulff in the field of properties of crystals, he begins the section "Physical crystallography" with a photograph of Yuri Viktorovich Wulff and the dates of his life (Fig. 5).
![[Fig. 5]](https://www.iucr.org/__data/assets/image/0007/154987/Fig-5.jpg)
Unfortunately, the successful work of Wulff, initiated in 1913, was interrupted by World War I, and then by the Russian October Revolution. Active scientific activity in Russia was suspended. At the behest of the times, during World War I (1914–1918), Wulff and his staff developed a new method of making X-ray screens for medical purposes. In Wulff’s X-ray research laboratory, almost all of the instruments and apparatus were made in the laboratory's workshop, and in 1912–1913 some of the equipment for working with X-rays was made by Wulff himself.
More than once Wulff was forced to abruptly change his difficult life of a Russian scientist in the midst of successful scientific work because of his high civic position. For example, soon after he had equipped a room for his scientific studies at Shanyavsky University, he again had to create everything anew within the walls of Moscow University after the October Revolution. In 1917, Wulff was reinstated as Privatdozent of the Department of Mineralogy at Moscow University, where he transferred his X-ray laboratory. In 1917, Wulff was elected a member of the Council of the Moscow P.N. Lebedev Physical Society, and since 1921 he was its chairman. In 1918 he became Professor of the Department of Mineralogy, Professor of the Department of Physics (1919–1925) and Professor of the Department of Crystallography (1922–1925) of the Faculty of Physics and Mathematics of Moscow University. In 1919, at the initiative of Wulff, the Institute for Physical and Chemical Research of Solid Matter was established at the Supreme Economic Council, in which he became director and head of the Department of Crystal Physics. In 1921, Wulff was elected a corresponding member of the Russian Academy of Science, and as a member of the Russian Academy of Artistic Sciences. In 1922, the Institute of Physics and Crystallography (later the Research Institute of Physics) was established at Moscow University, which was rightfully headed by Wulff.
During years of his creative studies in science, Wulff published more than 150 scientific and popular science works in Russia and abroad. Here are some of his main works: Crystals, Their Formation, Type and Structure (1917, 1926), Life of Crystals (1918), Fundamentals of Crystallography (1923), Guide to Crystallography (1904), Symmetry and its Manifestation in Nature. Lectures (1907), Practical Course in Geometric Crystallography with a Stereographic Grid (co-authored with A. V. Shubnikov, 1924).
It should be noted that Wulff, who was a man with broad scientific views, did a lot of pedagogical and educational work. He was the chairman of the Society for the Care of Students in the Tverskoy District of Moscow and the chairman of the Literacy Society in Tarusa, Kaluga province, as well as the chairman of the N.A. Umov Society for the Propagation of Physical Sciences. Wulff's work testifies to his great interest in the history of science. Possessing literary talent and the gift as a popularizer of science, in his books and lectures Wulff spoke about the history and successes of science. His reports were always accompanied by spectacular demonstrations. He contributed to the history of science with works on the work of such scientists as R. J. Haüy (1922), P. N. Lebedev (1912) and Nobel laureates W. H. Bragg and W. L. Bragg (1916).
In lectures on crystallography, Wulff used microprojections, which made it possible to immediately reproduce and visually demonstrate the phenomena that occur during the growth and development of crystals. He taught various courses: "On the Phenomena of Crystallization", "General Course of Crystallography for Mathematicians and Physicists", "The Theory of the External Shape of Crystals", "X-Ray Methods for the Study of Crystals", "Special Issues of Crystallography", "Introduction to Crystallography", "Crystal Physics", "Thermal Analysis as Applied to Mineralogy".
Wulff educated worthy disciples, who followed his trends and traditions in science: most close to him were A. V. Shubnikov (piezoelectricity and crystal optics), E. E. Flint (geometric crystallography) and S. A. Veiberg (crystal growth). Wulff's desire to convince crystallographers that this science (crystallography) is a part of solid-state physics was later confirmed and continued in the work of Academician A. V. Shubnikov. After Wulff's death, he developed his crystal physics direction and the direction associated with the symmetry of crystals. In 1943, the Laboratory of Crystallography, created by A. V. Shubnikov, was transformed into the Institute of Crystallography of the USSR Academy of Sciences, which he headed from the moment of its creation until 1962. And it is no coincidence that the institute now bears the name of Academician A. V. Shubnikov.
It is also known that, in addition to science, Wulff was fond of music and theater, vocals and photography. In the last years of his life, since 1914, Wulff spent every summer with his creative family in Tarusa at the rented suburban dacha "Pesochnoe". It was the dacha where the Tsvetaev family used to live, and where the artist V. E. Borisov-Musatov also lived and worked. This house became not only the study of the scientist but also the center of the cultural life of Tarusa. The Wulffs organized "Musical Subbotniks" at their dacha, giving free concerts of classical and folk music. Wulff himself also took part in these evenings, performing romances to the accompaniment of his wife, Vera (Fig. 6).
![[Fig. 6]](https://www.iucr.org/__data/assets/image/0008/154988/Fig-6.jpg)
The scientist was very musical and had a pleasant baritone, which allowed him to participate in operas that were staged in Polenovo and in the People's House in Tarusa. Thanks to the efforts of the Wulff family, autumn exhibitions of artists were organized. In memory of these amazing and talented people, in November 2016, the Tarusa Museum of Local Lore hosted an express exhibition dedicated to the 145th anniversary of the birth of the artist and musician Vera Wulff and her famous husband Georg Wulff. Vera had instilled in her children a love of the arts. Their elder son, Vladimir, became a professional pianist, and the younger, Boris, an artist. Boris's talents came to fruition when he was about 30, when he found himself abroad after World War I and the October Revolution.
It should be noted that the picturesque town of Tarusa on the banks of the beautiful Oka river has always attracted talented creative people – writers, poets, artists and musicians (K. G. Paustovsky, M. I. Tsvetaeva, V. D. Polenov, S. T. Richter and others).
It is interesting that Professor Wulff himself preferred the name of Georg, Georg (Prof. G.V. Wulff) as the author of his books, but both names of Professor Wulff are used in the literature - Georg and Yuri. According to his will, he was buried in the town of Tarusa above the Oka River (Kaluga Region) next to his wife, Vera (1871–1923). The monument over his final resting place bears the Cyrillic inscription (which reads as): “Fizik-kristallograf, chlen-korrespondent AN SSSR Yurii Viktorovich Vulf (1863–1925)" [Physicist-crystallographer, Corresponding Member of the Academy of Sciences of the USSR, Yuri Viktorovich Wulff (1863–1925)]. Later, their son Vladimir was also buried there (Fig. 7).
![[Fig. 7]](https://www.iucr.org/__data/assets/image/0009/154989/Fig-7.jpg)
A handsome and noble man with a broad outlook, who was in love with science and art, will remain in history with achievements bearing his name and with the good memories of his disciples and followers (Fig. 8).
![[Fig. 8]](https://www.iucr.org/__data/assets/image/0010/154990/Fig-8.jpg)
A lot has been written about Georg Viktorovich Wulff, an outstanding Russian physicist, one of the greatest crystallographers (see references). Most fully and interestingly Wulff's creative life is presented in the book by A. S. Sonin. Nevertheless, there remains an impression that his contribution to the development of science is underestimated. His life coincided with revolutionary events in the world and in science, which changed his life and scientific destiny more than once. Georg Wulff turned out to be one of the outstanding scientists in the constellation of world-renowned scientists such as Fedorov, Groth, Laue and the Braggs. They communicated closely and jointly moved science, making great discoveries for the benefit of science and humankind. In 1924, shortly before his death, Wulff traveled to Germany, England and France, where he spoke with the leading crystallographers M. Laue, W. L. and W. H. Bragg, M. Myers and others, and in Paris he made a report on his work in the field of crystal physics.
Сонин, А. С. (2001). "Георгий Викторович Вульф. 1863–1925". М.: Наука.
Sonin, A. S. (2001). "Georgiy Viktorovich Vulf. 1863–1925". M.: Nauka.
Храмов Ю. А. (1983). Вульф Георгий (Юрий) Викторович. Физики: Биографический справочник под ред. А. И. Ахиезера. Изд. 2-е, испр. и доп., М.: Наука.
Khramov, Yu. A. (1983). "Vulf Georgiy (Yuriy) Viktorovich. Fiziki: Biograficheskiy spravochnik (Physicists: A Biographical Directory). 2nd ed. M.: Nauka.
Щербаков, Р. Н. (2013). Стремление и любовь к научной истине. К 150-летию со дня рождения члена-корреспондента РАН Г.Н. Вульфа. ВЕСТНИК РОССИЙСКОЙ АКАДЕМИИ НАУК, 83(6), 562–569.
Shcherbakov, R. N. (2013). "Stremleniye i lyubov k nauchnoy istine. K 150-letiyu so dnya rozhdeniya chlena-korrespondenta RAN G.N. Vulfa" ("The pursuit and love of scientific truth. On the occasion of the 150th anniversary of the birth of Corresponding Member of the Russian Academy of Sciences G.N. Wulff"). Vestnik Rossiyskoy Akademii Nauk, 83(6), 562–569.
Памяти Георгия Викторовича Вульфа (2014). КРИСТАЛЛОГРАФИЯ, 59(3), 494–497.
"Pamyati Georgiya Viktorovicha Vulfa" ("In memory of Georg Viktorovich Wulff") (2014). Kristallografiya, 59(3), 494–497.
Frank-Kamenetsky, V. A. "WULFF, GEORG (YURI VIKTOROVICH)".
Вульф, Г.В. Автобиография от 22 ноября 1921 г. Архив Академии Наук СССР, фонд 1, onись 1-1921, дело 11, листы 47–49, Автограф.
Vulf, G. V. Autobiography dated 22 November 1921. Archive of the USSR Academy of Sciences, fund 1, inventory 1-1921, file 11, sheets 47–49, autograph.
Жданов, Г. С. (1987). 75летие открытия дифракции рентгеновских лучей. Успехи физ. наук. 153(4).
Zhdanov, G. S. (1987). "75-letiye otkrytiya difraktsii rentgenovskikh luchey" ("75th Anniversary of the Discovery of X-ray Diffraction"). Uspekhi fiz. Nauk (Soviet Physics-Uspekhi). 153(4).
Шубников, А. В. (1975). То, что сохранила память. В кн.: Избранные труды по кристаллографии. М., С. 12, 18–20.
Shubnikov, A. V. (1975). "To, chto sokhranila pamyat" ("What is kept in memory"). "Izbrannyye trudy po kristallografii" ("Selected Works on Crystallography"). M., pp. 12, 18–20.
Флинт, Е. Е. (1951). Воспоминания о Ю.В. Вульфе. Тр. Ин-та кристаллографии АН СССР, 6, 3–14.
Flint, E. E. (1951). "Vospominaniya o Yu.V. Vul'fe" ("Memories of Yu.V. Wulff"). Trudy Instituta Kristallografii AN SSSR (Proc. Inst. Crystallogr. USSR Acad. Sci.), 6, 3–14.
Записка об учёных трудах профессора Московского университета Г.В.Вульфа. Декабрь 1921 г. // Архив Академии Наук СССР, фонд 1, onись la, дело 169. Приложение к § 201 протокола заседания ОС РАН 10 декабря 1921 г.
"Zapiska ob uchonykh trudakh professora Moskovskogo universiteta G.V.Vul'fa. Dekabr' 1921 g." ("Note on the scientific works of Professor of Moscow University G.V. Wolf. December 1921") // Arkhiv Akademii Nauk SSSR (Archive of the Academy of Sciences of the USSR), fund 1, inventory la, file 169. Appendix to § 201 of the minutes of the meeting of the OS RAS on 10 December 1921.
Человек дня: Георгий Вульф / «Полит.ру» – информационно-аналитический портал, 22 июня 2021.
"Chelovek dnya: Georgiy Vul'f" ("Person of the day: Georg Wulff"). Polit.ru - information and analytical portal, 22 June 2021.
Смолеговский, А. М. (2009). «У. Л. Брэгг и его роль в создании структурной кристаллохимии» Москва.
Smolegovskiy, A. M. (2009). "U. L. Bregg i yego rol' v sozdanii strukturnoy kristallokhimii" ("W. L. Bragg and his role in the creation of structural crystal chemistry"). M.
Болдырев, А. К. (1926). Основы Кристаллографии» Издание КУБУЧ’а. Ленинград.
Boldyrev, A. K. (1926). Osnovy Kristallografii (Fundamentals of Crystallography). KUBUCH edition. Leningrad.
Болдырев, А. К. (1934). Кристаллография. ОНТИ.НКТП.СССР. Государственное научно-техническое горно-геолого-нефтяное издательство. Ленинград, Москва, Грозный, Новосибирск.
Boldyrev, A. K. (1934). Kristallografiya (Crystallography). ONTI NKTP SSSR. Leningrad, Moscow, Grozny, Novosibirsk.
Кузнецов, В. Д. (1937). «Физика твёрдого тела», 2 изд., т. 1. Томск.
Kuznetsov, V. D. (1937). Solid State Physics, 2nd ed., Vol. 1. Tomsk.
Some of Wulff’s writings on crystallophysics and crystallography were collected as lzbrannye raboty po kristallofizike i kristallografi (Selected Works in Crystallophysics and Crystallography, Moscow, 1952).
Separately published early works include “Opytnoe issledovanie elektricheskikh svoystv kvartsa” (“Experimental Investigation of the Electrical Properties of Quartz”). Varshavskia universitetskia izvestia, 3 (1886), 1–17;
“O stroenii kristallov kvartsa” (“On the Structure of Quartz Crystals”) in Zapiski Imperatorskago mineralogicheskago obschestva, 2nd ed., series 25 (1889), 341–342;
“Ob uproshchenii kristallograficheskikh vychisleny” (“On the Simplification of Crystallographic Computation”) ibid., 29 (1892), 58–64;
“Svoystva nekotorykh psevdosimmetricheskikh kristallov v svyazi s teoriey kristallicheskogo stroenia veshchestva” (“Properties of Certain Pseudosymmetrical Crystals in Relation to the Theory of the Crystal Structure of Matter”) ibid., 29 (1892), 65–130,
his master’s thesis: “K voprosu o skorostyakh rosta i rastvorenia kristallicheskikh graney” (“On the Question of the Velocity of Growth and Dissolution of Crystal Faces”), in Varshavskia universitetskia izvestia, 7 (1895), 1–40; 8 (1895), 41–56; n.s., 1 (1896), 57–88; 2 (1896), 89–122; his doctoral dissertation also in German in Z. Kristallogr. Mineral. 34 (1901), 449–530;
“Die Symmetrieebene als Grundelement der Symmetrie,” ibid, 27 (1897), 556–558;
“Untersuchungen im Gebiete der optischen Eigenschaften isomorpher Krystalle,” ibid., 36 (1902), 1–28;
“Ein Beitrag zur Theodolithmethode,” ibid., 37 (1903), 50–56; and
“Untersuchungen über die Genauigkeitsgrenzen der Gesetze der geometrischen Krystallographie,” ibid., 38 (1904), 1–57; and Rukovodstvo po kristallografii (Guide to Crystallography), Warsaw, 1904.
Subsequent works were Simmetria i ee proyavlenia v prirode (Symmetry and Its Appearance in Nature), Moscow, 1908;
“Über die Krystallisation des Kaliumjodods auf dem Glimmer”. Z. Kristallogr. Mineral. 45 (1908), 335–345;
“Zur Theorie des Krystallhabitus,” ibid., 433–472;
“Über die Natur ‘flussiger’ und ‘fliessender’ Krystalle,” ibid., 46 (1909), 261–265;
“Über die Kristallröntgenogramme”. Phys. Z. 14 (1913), 217–222;
“O kapillyarnoy teorii formy kristallov” (“On the Capillary Theory of Crystal Forms”), in Zhurnal Russkago fiziko khimicheskago obshchestva pri Imperatorskom St–Peterburgskom universitete, 48 (1916), 337–349;
Kristally, ikh obrazovanie, vid i stroenie (Crystals, Their Formation, Type and Structure), Moscow, 1917; 2nd ed., edited and annotated by M. M. and S. Sabshnikov, 1926);
Zhizn crystallov (The Life of Crystals), Moscow, 1918;
Osnovy kristallografii (Principles of Crystallography), Moscow, 1923, 2nd ed., 1926;
Praktichesky kurs geometricheskoy kristallografü so steregraficheskoy setkoy (“Practical Course in Geometrical Crystallography with a Stereographic Net”), Moscow, 1924; and
“O molekulyarnoy strukture muskovita” (“On the Molecular Structure of Muscovite”), Trudy Instituta prikladnoi mineralogii i metallurgii, 25 (1926), 22–29.
On Wulff and his work, see Leleyn, G. G. & Kirsanov, G. A. (1951). “Khronologichesky ukazatel trudov Y. V. Vulfa” (“Chronological Guide to the Works of Y. V. Vulf”). Trudy Instituta kristallografii. Akademiys nauk SSSR, 6, 15–24
and von Laue, M. (1943). "Der Wulffsche Satz für die Gleichgewichtsform von Kristallen". Z. Kristallogr. Mineral. 105, 124–133.
Larissa Zasurskaya is located at the Chemistry Department of Moscow State University, Russia.
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