Atomic-Level Characterization of Dynamics of a 3D Covalent Organic

Communication Cite This: J. Am. Chem. Soc. 2019, 141, 10962−10966

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Atomic-Level Characterization of Dynamics of a 3D Covalent Organic Framework by Cryo-Electron Diffraction Tomography Tu Sun,† Lei Wei,† Yichong Chen, Yanhang Ma,* and Yue-Biao Zhang* School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China

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S Supporting Information *

high crystallinity, phase purity, and morphological homogeneity, which allowed us to uncover its guest-dependent dynamics though high-resolution powder X-ray diffraction (PXRD) and Rietveld refinements. Since it exhibited crystal contraction upon adsorption of water and crystal expansion upon inclusion of organic molecules, respectively, we envisage that such a sample would be an ideal candidate sample for demonstrating the atomic-level characterization of dynamics using EDT. Learning from biomacromolecules and other sensitive materials, the sample plunge-freezing and cryogenic transfer protocols10 are implemented here for the first time in COF chemistry. When preparing the sample (Section S1), COF microcrystals (Figure S1) were readily dispersed in water or organic solvents by ultrasonication and then drop-cast on a copper grid coated with an ultrathin carbon film. To study the activated phase COF-300-V, the grid was loaded on a high-tilt TEM (cryo-)holder and then evacuated in a pump station overnight to fully remove the guest molecules. To study the hydrated phase COF-300-H2O, the grid was plunge-frozen in liquid ethane (185 K) using a Vitrobot and stored in liquid nitrogen (77 K). The grid remained in liquid nitrogen as it was transferred to the cryo-holder. To study the expanded phase, the COF was soaked in tetrahydrofuran (THF), 1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid (IL), or poly(methyl methacrylate) (PMMA, Figure S2) (termed COF-300-THF, COF-300-IL, and COF-300PMMA, respectively). The EDT data were automatically collected by combining a goniometer rotation and electron-beam tilt with a precise step of 0.1/0.2°.11 To reduce the electron beam dose and to balance the diffraction intensity, the spot size and exposure time were optimized (Section S2). All of the collected electron diffraction frames were used to reconstruct the 3D reciprocal space (Figure 1). For the activated COF-300-V, we first collected EDT data on a single crystal sized ∼1 μm (Figure 1a) without a cryo-holder. The crystallinity of the COF decayed during the data collection as seen in the diffraction patterns (Figure S3). The overall EDT data show strong diffraction and relatively high resolution up to 1.1 Å, but the completeness is limited (Figure 1b), indicating the electron beam damage of the COF crystals at room temperature despite their high crystallinity. In light of this damage, further EDT data collection was performed with a cryo-transfer holder, which improves sample

ABSTRACT: Understanding the dynamics of covalent organic frameworks (COFs) is desirable for developing smart materials with coherent responses to external stimulus. Here we illustrate the structural determination of dynamics at atomic level by cryo-electron diffraction tomography (EDT) with single crystals of COF-300 having only submicrometer sizes. We observe and elucidate the crystal contraction upon H2O adsorption by ab initio structural solution of all non-hydrogen atoms of framework and unambiguous location of guest molecules in the pores. We also observe the crystal expansion of COF-300 upon inclusion of ionic liquid or polymer synthesized in the channels, whose conformational aspects of frameworks can be confirmed.

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tomic-level characterization of covalent organic frameworks (COFs) is essential to understanding their pore chemistry and framework adaptability.1 The recent reported study of COFs through single-crystal X-ray diffraction (SXRD) is an example of how guests, and their aggregation, can be observed, allowing their impact on the host material to be evaluated.2 Indeed, studying COF dynamics with this level of accuracy would provide valuable information on their stimuli responsive properties.3,4 Owing to the insufficient reversibility of bond formation and time-intensive single-crystal growth, the majority of COFs, with different topologies or linkages,5,6 still face difficulty in growing large single crystals (>20 μm) suitable for SXRD. In this report, we reveal how electron diffraction tomography (EDT) with cryogenic protocols can shed light on the structure dynamics of a 3D COF at this requisite atomic level. Relative to X-ray photons, the stronger interaction of electrons with matter allows structural determination by EDT of crystals only hundreds of nanometers in size.7,8 This method has previously been successfully applied to elucidate the crystal structure of COFs,7 but most of the diffraction resolution have been limited to 1.5 Å.9 This limitation prevented the ab initio structural resolution and hampered determination of framework conformation and guest molecule arrangement at atomic-level. On the way to determine the dynamics of COFs, there are still several challenges: (1) poor crystallinity and aggregation of COF crystals; (2) electron beam sensitivity of sample to the electron beam; and (3) loss of guest molecules under ultrahigh vacuum in TEM. Recently, we have developed a facile and scalable synthetic protocol of COF-300 to obtain dispersed microcrystals with © 2019 American Chemical Society

Received: May 7, 2019 Published: June 26, 2019 10962

DOI: 10.1021/jacs.9b04895 J. Am. Chem. Soc. 2019, 141, 10962−10966

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Figure 1. Atomic-level characterization of dynamics through electron diffraction tomography illustrated by COF-300 with single crystals at only micrometer size. The TEM images of the single crystals and the EDT data projected along the [100] or [010] direction for the activated phase COF-300-V with routine holder (a,b) and with cryo-holder (c,d) and hydrated phase COF-300-H2O (e,f) and expanded phase COF-300-PMMA (g,h).

stability under the electron beam. Diffraction resolution with the cryo-transfer holder was not compromised during data collection (Figure S4). This resiliency allowed us to perform electron diffraction on COF crystals with better than 1.0 Å resolution (Figure 1d). From the reconstructed 3D lattice in reciprocal space, the lattice constants were determined to be a = b = 20.5 Å, c = 9.1 Å, α = β = γ = 90°, V = 3824.3 Å3. The reflection conditions were summarized as hkl: h + k + l = 2n; hk0: h, k = 2n; 0kl: k + l = 2n (Figure S5), which suggested two possible space groups in tetragonal crystal system: I41/a (no. 88) and I41/amd (no. 141). The crystal structure of COF-300V was found to belong to the space group I41/a using the direct method, and all non-hydrogen atoms were located from the electrostatic potential map (Figure 2a,d). For the hydrated phase COF-300-H2O, we dispersed activated COF-300 in water and drop-cast it on the grid, followed by the plunge-freezing protocol for avoiding the crystallization of ice. We observed only a small amount of vitrified water attached to the sample (Figure 1e), which only slightly increases the background of the EDT data (Figures 1f and S6). The resolution of the overall EDT data improved to exceed 0.8 Å, and the completeness also improved from 50% to 79%, which suggests the guest molecules serve to stabilize the framework (Figure S7). The crystal retained its tetragonal space group I41/a (no. 88, Figure S8), but the unit cell shrinks to a = b = 19.9 Å, c = 9.3 Å, α = β = γ = 90°, V = 3682.9 Å3 with a volume contraction of about 3.7%. Combined with ab initio structure solution using direct methods, all non-hydrogen atoms of the framework and the locations of guest molecules were therefore determined by cryo-EDT in COF chemistry for the first time (Figure 2b). For the expanded phase, we first examined the sample immersed in THF using the cryo-transfer holder. However, the diffraction decayed quickly, preventing successful collection of

a data set. We also attempted to include the ionic liquid into the COF5d but found it difficult to guarantee full inclusion and crystal dispersion. Thus, although the SEM and TEM images (Figure S9) show the swelling of COF crystals, the resolution of the EDT data set is limited to 1.8 Å (Figure S10). We finally tried to include monomers of PMMA into the COF and polymerize them in the channel. This method provided a more stable sample of the expanded phase of COF-300-PMMA for EDT data collection. The resolution of EDT data was improved to 1.5 Å (Figure 1h), and we are able to clearly observe a changed unit cell a = b = 27.3 Å, c = 7.7 Å, α = β = γ = 90°, V = 5738.7 Å3, which shows a significant crystal volume expansion as large as 50% without symmetry change (Figure S11). This is consistent with the aspect ratio change of the microcrystal (Figure 1g), which allows us to observe the 4-fold rotation symmetry along the c axis by titling the crystal and recording the selected-area electron diffraction pattern along the [001] zone axis (Figure S12). Although ab initio structural solution was not available for the expanded phase, we could also obtain its electrostatic potential map (Figure 2c) at lower resolution by phasing with a rigid-constraint model. With such cryo-EDT data on single microcrystals, combined with ab initio structural solutions and/or rigid-constraint refinements, we are therefore able to unravel atomic-level dynamics of the activated, hydrated, and expanded phases of COF-300 (Section S3). Due to the technical difficulty of dynamical refinements,12 the crystal structures were refined against EDT data based on the kinematical assumption and geometric restraints applied on the aromatic rings. All of the hydrogen atoms were geometrically added and refined using the riding mode. As shown in Figure 2, the contraction and expansion of the crystals originate from the leverage edges between the tetrahedral centers. The geometric deformation of the 10963

DOI: 10.1021/jacs.9b04895 J. Am. Chem. Soc. 2019, 141, 10962−10966

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Figure 2. Potential density maps and crystal structures and of COF-300-V (a,d), COF-300-H2O (b,e), and COF-300-PMMA (c,f) revealed by the cryo-EDT data and structural refinements. We illustrate here the atomic level characterize of dynamics by cryo-EDT for the first time in COF chemistry, showing its great potential in the visualization of pore reaction and framework adaptability with only micrometer-sized single crystals.

tetrahedral building block and the conformation change of the organic linkers (−ph-NC-ph-CN-ph−) were thus observed (Table S11). These results reveals that such structural transformation from the confirmation change of the imine bonds might provide more robustness for dynamics4b through the revolving bond rather than mechanical stretching. In the structure of COF-300-H2O, the distance between two adjacent oxygen atoms of H2O in the channels is 2.952 Å, and the separation from each oxygen atom to its closest nitrogen atom of the imine bond on the wall is 3.089 Å, which indicates that

there is only weak interaction driving the framework adapting to the helix chains of water linked by hydrogen bonding (Figure S20). Although the resolution of the structure of COF300-PMMA is limited, the structure is refined with rigid constraints resulting in decent convergence. The residual of the electrostatic potential in the channel can be seen by Fourier difference maps (Figure 2f). We are therefore able to model the PMMA chain in the pore (Figure S21), which reveals four chains are possibly included in one channel and therefore enforced the framework to an expanded phase. 10964

DOI: 10.1021/jacs.9b04895 J. Am. Chem. Soc. 2019, 141, 10962−10966

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K. W.; Auras, F.; Bein, T. Molecular Docking Sites Designed for the Generation of Highly Crystalline Covalent Organic Frameworks. Nat. Chem. 2016, 8, 310. (b) Zhang, Y.; Duan, J.; Ma, D.; Li, P.; Li, S.; Li, H.; Zhou, J.; Ma, X.; Feng, X.; Wang, B. Three-Dimensional Anionic Cyclodextrin-Based Covalent Organic Frameworks. Angew. Chem., Int. Ed. 2017, 56, 16313. (c) Han, X.; Huang, J.; Yuan, C.; Liu, Y.; Cui, Y. Chiral 3D Covalent Organic Frameworks for High Performance Liquid Chromatographic Enantioseparation. J. Am. Chem. Soc. 2018, 140, 892. (d) Guan, X.; Ma, Y.; Li, H.; Yusran, Y.; Xue, M.; Fang, Q.; Yan, Y.; Valtchev, V.; Qiu, S. Fast, Ambient Temperature and Pressure Ionothermal Synthesis of Three-Dimensional Covalent Organic Frameworks. J. Am. Chem. Soc. 2018, 140, 4494. (6) (a) Uribe-Romo, F. J.; Doonan, C. J.; Furukawa, H.; Oisaki, K.; Yaghi, O. M. Crystalline Covalent Organic Frameworks with Hydrazone Linkages. J. Am. Chem. Soc. 2011, 133, 11478. (b) Jackson, K. T.; Reich, T. E.; El-Kaderi, H. M. Targeted synthesis of a porous borazine-linked covalent organic framework. Chem. Commun. 2012, 48, 8823. (c) Kandambeth, S.; Mallick, A.; Lukose, B.; Mane, M. V.; Heine, T.; Banerjee, R. Construction of Crystalline 2D Covalent Organic Frameworks with Remarkable Chemical (Acid/Base) Stability via a Combined Reversible and Irreversible Route. J. Am. Chem. Soc. 2012, 134, 19524. (d) Guo, J.; Xu, Y.; Jin, S.; Chen, L.; Kaji, T.; Honsho, Y.; Addicoat, M. A.; Kim, J.; Saeki, A.; Ihee, H.; Seki, S.; Irle, S.; Hiramoto, M.; Gao, J.; Jiang, D. Conjugated organic framework with three-dimensionally ordered stable structure and delocalized π clouds. Nat. Commun. 2013, 4, 2736. (f) Fang, Q.; Zhuang, Z.; Gu, S.; Kaspar, R. B.; Zheng, J.; Wang, J.; Qiu, S.; Yan, Y. Designed synthesis of large-pore crystalline polyimide covalent organic frameworks. Nat. Commun. 2014, 5, 4503. (g) Du, Y.; Yang, H.; Whiteley, J. M.; Wan, S.; Jin, Y.; Lee, S.-H.; Zhang, W. Ionic Covalent Organic Frameworks with Spiroborate Linkage. Angew. Chem., Int. Ed. 2016, 55, 1737. (h) Pyles, D. A.; Crowe, J. W.; Baldwin, L. A.; McGrier, P. L. Synthesis of Benzobisoxazole-Linked Two-Dimensional Covalent Organic Frameworks and Their Carbon Dioxide Capture Properties. ACS Macro Lett. 2016, 5, 1055. (i) Jin, E.; Asada, M.; Xu, Q.; Dalapati, S.; Addicoat, M. A.; Brady, M. A.; Xu, H.; Nakamura, T.; Heine, T.; Chen, Q.; Jiang, D. Two-Dimensional sp2 Carbon−Conjugated Covalent Organic Frameworks. Science 2017, 357, 673. (j) Roeser, J.; Prill, D.; Bojdys, M. J.; Fayon, P.; Trewin, A.; Fitch, A. N.; Schmidt, M. U.; Thomas, A. Anionic silicate organic frameworks constructed from hexacoordinate silicon centres. Nat. Chem. 2017, 9, 977. (k) Stewart, D.; Antypov, D.; Dyer, M. S.; Pitcher, M. J.; Katsoulidis, A. P.; Chater, P. A.; Blanc, F.; Rosseinsky, M. J. Stable and ordered amide frameworks synthesised under reversible conditions which facilitate error checking. Nat. Commun. 2017, 8, 1102. (l) Li, L. H.; Feng, X. L.; Cui, X. H.; Ma, Y. X.; Ding, S. Y.; Wang, W. Salen-Based Covalent Organic Framework. J. Am. Chem. Soc. 2017, 139, 6042. (m) Zhao, C.; Diercks, C. S.; Zhu, C.; Hanikel, N.; Pei, X.; Yaghi, O. M. Urea-Linked Covalent Organic Frameworks. J. Am. Chem. Soc. 2018, 140, 16438. (n) Zhang, B.; Wei, M.; Mao, H.; Pei, X.; Alshmimri, S. A.; Reimer, J. A.; Yaghi, O. M. Crystalline Dioxin-Linked Covalent Organic Frameworks from Irreversible Reactions. J. Am. Chem. Soc. 2018, 140, 12715. (o) Haase, F. H.; Troschke, E.; Savasci, G.; Banerjee, T.; Duppel, V.; Dorfler, S.; Grundei, M. M. J.; Burow, A. M.; Ochsenfeld, C.; Kasel, S.; Lotsch, B. V. Topochemical conversion of an imine- into a thiazole-linked covalent organic framework enabling real structure analysis. Nat. Commun. 2018, 9, 2600. (7) (a) Zhang, Y.-B.; Su, J.; Furukawa, H.; Yun, Y.; Gándara, F.; Duong, A.; Zou, X.; Yaghi, O. M. Single-Crystal Structure of a Covalent Organic Framework. J. Am. Chem. Soc. 2013, 135, 16336. (b) Liu, Y.; Ma, Y.; Zhao, Y.; Sun, X.; Gándara, F.; Furukawa, H.; Liu, Z.; Zhu, H.; Zhu, C.; Suenaga, K.; Oleynikov, P.; Alshammari, A. S.; Zhang, X.; Terasaki, O.; Yaghi, O. M. Weaving of Organic Threads into a Crystalline Covalent Organic Framework. Science 2016, 351, 365. (c) Liu, Y.; Ma, Y.; Yang, J.; Diercks, C. S.; Tamura, N.; Jin, F.; Yaghi, O. M. Molecular Weaving of Covalent Organic Frameworks for Adaptive Guest Inclusion. J. Am. Chem. Soc. 2018, 140, 16015. (d) Ma, T.; Li, J.; Niu, J.; Zhang, L.; Etman, A. S.; Lin, C.; Shi, D.;

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.9b04895. Sample preparation, data collection and structure analysis (PDF) EDT crystal structure of COF-300-V (CIF) Cryo-EDT crystal structure of COF-300-V (CIF) Cryo-EDT crystal structure of COF-300-H2O (CIF) Cryo-EDT crystal structure of COF-300-IL (CIF) Cryo-EDT crystal structure of COF-300-PMMA (CIF) Reconstructed ED pattern of COF-300-V (MP4) Reconstructed ED pattern of COF-300-H2O (MP4)

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AUTHOR INFORMATION

Corresponding Authors

*[email protected] *[email protected] ORCID

Yue-Biao Zhang: 0000-0002-8270-1067 Author Contributions †

These authors contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by the National Natural Science Foundation of China (No. 21522105, 21875140, and 51861145313). The authors thank Dr. P. Oleynikov, Prof. O. Terasaki, and CℏEM SPST, ShanghaiTech University (#EM02161943) for scientific and financial support of EM facilities, Dr. F. Luo and Prof. C. Liu at IRCBC-CAS for technical support in sample plunge-freezing, and Prof. F. Tsung at Boston College for beneficial discussion. Y.M. thanks the Commission for Science and Technology of Shanghai Municipality (17ZR1418600) and the Young Elite Scientist Sponsorship Program by CAST (2017QNRC001).

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REFERENCES

(1) El-Kaderi, H. M.; Hunt, J. R.; Mendoza-Cortés, J. L.; Côté, A. P.; Taylor, R. E.; O’Keeffe, M.; Yaghi, O. M. Designed Synthesis of 3D Covalent Organic Frameworks. Science 2007, 316, 268. (2) Ma, T.; Kapustin, E. A.; Yin, S. X.; Liang, L.; Zhou, Z.; Niu, J.; Li, L.-H.; Wang, Y.; Su, J.; Li, J.; Wang, X.; Wang, W. D.; Wang, W.; Sun, J.; Yaghi, O. M. Single-Crystal X-ray diffraction structures of covalent organic frameworks. Science 2018, 361, 48. (3) (a) Uribe-Romo, F. J.; Hunt, J. R.; Furukawa, H.; Klock, C.; O’Keeffe, M.; Yaghi, O. M. A Crystalline Imine-Linked 3-D Porous Covalent Organic Framework. J. Am. Chem. Soc. 2009, 131, 4570. (b) Liu, Y.; Ma, Y.; Yang, J.; Diercks, C. S.; Tamura, N.; Jin, F.; Yaghi, O. M. Molecular Weaving of Covalent Organic Frameworks for Adaptive Guest Inclusion. J. Am. Chem. Soc. 2018, 140, 16015. (4) (a) Ma, Y.-X.; Li, Z.-J.; Wei, L.; Ding, S.-Y.; Zhang, Y.-B.; Wang, W. A Dynamic Three-Dimensional Covalent Organic Framework. J. Am. Chem. Soc. 2017, 139, 4995. (b) Chen, Y.; Shi, Z.; Wei, L.; Zhou, B.; Tan, J.; Zhou, H.-L.; Zhang, Y.-B. Guest-Dependent Dynamics in a 3D Covalent Organic Framework. J. Am. Chem. Soc. 2019, 141, 3298. (c) Sun, Q.; Aguila, B.; Perman, J. A.; Nguyen, N. T.-K.; Ma, S. Flexibility Matters: Cooperative Active Sites in Covalent Organic Framework and Threaded Ionic Polymer. J. Am. Chem. Soc. 2016, 138, 15790. (5) (a) Ascherl, L.; Sick, T.; Margraf, J. T.; Lapidus, S. H.; Calik, M.; Hettstedt, C.; Karaghiosoff, K.; Döblinger, M.; Clark, T.; Chapman, 10965

DOI: 10.1021/jacs.9b04895 J. Am. Chem. Soc. 2019, 141, 10962−10966

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Journal of the American Chemical Society Chen, P.; Li, L.-H.; Du, X.; Sun, J.; Wang, W. Observation of Interpenetration Isomerism in Covalent Organic Frameworks. J. Am. Chem. Soc. 2018, 140, 6763. (e) Ding, H. M.; Li, J.; Xie, G. H.; Lin, G. Q.; Chen, R. F.; Peng, Z. K.; Yang, C. L.; Wang, B. S.; Sun, J. L.; Wang, C. An AIEgen-based 3D covalent organic framework for white light-emitting diodes. Nat. Commun. 2018, 9, 5234. (8) (a) Denysenko, D.; Grzywa, M.; Tonigold, M.; Streppel, B.; Krkljus, I.; Hirscher, M.; Mugnaioli, E.; Kolb, U.; Hanss, J.; Volkmer, D. Elucidating Gating Effects for Hydrogen Sorption in MFU-4-Type Triazolate-Based Metal−Organic Frameworks Featuring Different Pore Sizes. Chem. - Eur. J. 2011, 17, 1837. (b) Feng, D.; Wang, K.; Su, J.; Liu, T. F.; Park, J.; Wei, Z.; Bosch, M.; Yakovenko, A.; Zou, X.; Zhou, H. C. Highly Stable Zeotype Mesoporous Zirconium Metal− Organic Framework with Ultralarge Pores. Angew. Chem., Int. Ed. 2015, 54, 149. (c) Yuan, S.; Qin, J. S.; Xu, H. Q.; Su, J.; Rossi, D.; Chen, Y.; Zhang, L.; Lollar, C.; Wang, Q.; Jiang, H. L.; Son, D. H.; Xu, H.; Huang, Z.; Zou, X.; Zhou, H. C. [Ti8Zr2O12(COO)16] Cluster: An Ideal Inorganic Building Unit for Photoactive Metal− Organic Frameworks. ACS Cent. Sci. 2018, 4, 105. (9) During the revision of this manuscript, atomic determination of 3D COFs using cRED was reported. Wang, C.; Gao, C.; Li, J.; Yin, S.; Lin, G.; Ma, T.; Meng, Y.; Sun, J. Isostructural 3D Covalent Organic Frameworks. Angew. Chem., Int. Ed. 2019, 58, 1630. (10) (a) Fleck, R. A. Low-Temperature Electron Microscopy: Techniques and Protocols. In Cryopreservation and Freeze-Drying Protocols. Methods in Molecular Biology: Methods and Protocols; Wolkers, W., Oldenhof, H., Eds.; Springer, New York, 2015; p 1257. (b) Li, Y.; Li, Y.; Pei, A.; Yan, K.; Sun, Y.; Wu, C.-L.; Joubert, L.-M.; Chin, R.; Koh, A. L.; Yu, Y.; Perrino, J.; Butz, B.; Chu, S.; Cui, Y. Atomic structure of sensitive battery materials and interfaces revealed by cryo−electron microscopy. Science 2017, 358, 506. (c) Luo, F.; Gui, X.; Zhou, H.; Gu, J.; Li, Y.; Liu, X.; Zhao, M.; Li, D.; Li, X.; Liu, C. Atomic structures of FUS LC domain segments reveal bases for reversible amyloid fibril formation. Nat. Struct. Mol. Biol. 2018, 25, 341. (11) Gemmi, M.; Oleynikov, P. Scanning reciprocal space for solving unknown structures: energy filtered diffraction tomography and rotation diffraction tomography methods. Z. Kristallogr. - Cryst. Mater. 2013, 228, 51. (12) Palatinus, L.; Brázda, P.; Boullay, P.; Perez, O.; Klementová, M.; Petit, S.; Eigner, V.; Zaarour, M.; Mintova, S. Hydrogen positions in single nanocrystals revealed by electron diffraction. Science 2017, 355, 166.

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