Weaving on the molecular scale

Although items exhibiting topology are ubiquitous in everyday life, the realization of at nanoscale level relies on innovative synthetic strategies. A molecular weaving strategy, recently reported Nature Chemistry and by Leigh co-workers, has outlined precise synthesis a 74 knot two-dimensional fabric. These breakthroughs hard heels each other open up new route for incorporating predictable, well-defined topologies into architectures. They will fuel exploitation advanced materials with topology-related properties. Weaving, time-honored skill born out united wisdom humanity, impacted profoundly many civilizations supported our lives from time immemorial. By guiding one-dimensional (1D) directional strands—such as fibers ropes—over under to form (2D) interlaced grids, large variety woven products have been created. Examples run gamut textiles, baskets, fishing nets traditional Chinese knots Celtic laces. During process, interwoven introduced materials, giving rise not only aesthetically pleasing fabrics, but also excellent macroscopic properties terms strength, resilience, porosity. The incorporation systems holds promise endowing resulting (1) analogous those that already discovered making textiles (2) unprecedented features beyond what can bring about. Stimulated this prospect, chemists scientists searching efficient methods weave linear molecules zig-zag conformations. interpenetration1Batten S.R. Robson R. Interpenetrating nets: Ordered, periodic entanglement.Angew. Chem. Int. Ed. 1998; 37: 1460-1494Crossref PubMed Scopus (4069) Google Scholar flexible networks serendipitously crystal structures—e.g., inorganic salts, metal coordination networks, porous polymers—the rational design structures feasible until recently, coincidentally when nanotopology2Stoddart J.F. Dawning age nanotopology.Nano Lett. 2020; 20: 5597-5600Crossref (24) Scholar,3Guo Q.-H. Jiao Y. Feng Stoddart nanotopology.CCS 2021; 3: 1542-1572Crossref (22) started be recognized discipline its own right. Thanks advent mechanical bond chemistry, emergence mechanically interlocked molecules,4Stoddart Mechanically (MIMs)—Molecular shuttles, switches, machines (Nobel lecture).Angew. 2017; 56: 11094-11125Crossref (477) growing awareness chemical topology,5Forgan R.S. Sauvage J.-P. Chemical topology: Complex knots, links, entanglements.Chem. Rev. 2011; 111: 5434-5464Crossref (596) past decade witnessed2Stoddart nanotopology. One increasingly vibrant research activities field lies extended networks. For example, Yaghi et al.6Liu Ma Zhao Sun X. Gándara F. Furukawa H. Liu Z. Zhu C. Suenaga K. al.Weaving organic threads crystalline covalent framework.Science. 2016; 351: 365-369Crossref (294) construction an framework combining Sauvage’s seminal work7Dietrich-Buchecker C.O. J.P. Kintzinger Une nouvelle famille de molecules: Les metallo-catenanes.Tetrahedron 1983; 24: 5095-5098Crossref (552) Cu(I)-templated bis-phenanthroline [2]catenates reticular chemistry.8Yaghi O.M. Kalmutzki M.J. Diercks C.S. Introduction Reticular Chemistry: Metal-Organic Frameworks Covalent Organic Frameworks. Wiley, Weinheim2019Crossref (252) Another major contribution was made Wennemers co-workers,9Lewandowska U. Zajaczkowski W. Corra S. Tanabe J. Borrmann Benetti E.M. Stappert Watanabe Ochs N.A.K. Schaeublin al.A triaxial supramolecular weave.Nat. 9: 1068-1072Crossref who invoked strategy produce assembly is held together noncovalent bonding interactions. Despite recent progress within frameworks,7Dietrich-Buchecker assemblies,9Lewandowska polymer networks,10Li G. Wang L. Wu Guo Bai Yan Woven via topological transformation [2]catenane.J. Am. Soc. 142: 14343-14349Crossref (15) it remains grand challenge develop practical strategies discrete small topologies. Recently, his co-workers11Leigh D.A. Danon J.J. Fielden S.D.P. Lemonnier J.-F. Whitehead G.F.S. Woltering S.L. endless (74) knot.Nat. 13: 117-122Crossref (29) proposed executed protocol their knot, feat had accomplished previously chemists. usually involves two-step procedure which pre-assembly building blocks prerequisite generation desired following subsequent ring-closing reactions. In contrast previous resulted mainly linear/circular helicates, appropriate precursor seven-crossing (74 Alexander–Briggs notation) [3 × 3] grid. difficulties faced during formation excessive strain generated process. This energetically unfavorable obstacle minimized through exquisite structural (Figure 1) ligand, e.g., strand 1, featuring use thiazolo[5,4-d]thiazole (TTZ) units adopt geometries. Specifically, 1 contains three tridentate sites octahedral Fe(II) ions, one able inner site combination two TTZ 4-dimethylaminopyridine group, while outer composed TTZ, benzimidazole, pyridine units. Furthermore, medium-length, alkene-terminated chains short enough guarantee intragrid—rather than intergrid—olefin metathesis, sufficiently long avoid additional ring closure. last all-important piece puzzle 2) grid templation tetrafluoroborate (BF4?) anions. Upon addition Fe(BF4)2 solution targeted [Fe916](BF4)18 formed quantitatively, probed variable temperature diffusion-ordered 1H NMR spectroscopy verified X-ray crystallography. It worth noting four BF4? anions accommodated square cavities between “weft” “warp” strands All B–F bonds anion point direction ions located corners squares, all fluorine atoms engaged close contacts centers electron-deficient thiazole rings. well-ordered arrangement confers stabilization upon result synergistic charge–dipole anion–? When subjected microwave irradiation 110°C presence second-generation Hoveyda–Grubbs catalyst demetallation competing ligands, transformed 3, accompanied macrocycle 4 Solomon link 5 byproducts. product 3 isolated cyclic gel permeation chromatography then identified combined electrospray ionization mass spectrometry spectroscopy. 7% overall yield unreasonable, given fact connections adjacent ends proceed different possible pathways, leads 3. limited selectivity needs overcome comes larger (e.g., [5 5] or [7 7]) grids using longer strands. represents first implementation knots. basic motif smallest lace. Shortly afterward, al.12August D.P. Dryfe R.A.W. Haigh S.J. Kent P.R.C. Li Muryn C.A. Palmer L.I. Song al.Self-assembly layered molecularly fabric.Nature. 588: 429-435Crossref (26) implemented similar construct 2D fabric intergrid pre-assembled grids. oxidation thiols disulfides chosen crosslinking reaction, account effectiveness condensed matter reagent waste transformation—i.e., O2 H2O, respectively—can both diffuse solid material. To end, thiol-terminated 2, bearing same used block, treated “woven tile,” namely [Fe926](BF4)18. exposed air, slow precipitation [Fe926](BF4)18 oxidative thiol groups disulfide induced leading formation, over course days, films microcrystalline particles surface reaction vessel. were KCN remove ion templates, thereafter washed solvents, affording wholly 6. Both scanning electron microscopy atomic force showed sheet morphology 6 dimensions few hundreds micrometers length width, around nanometers thick. long-range order material confirmed scattering analyses phenomenon birefringence. Compared non-woven constructed enhanced strength topologically constrained alignment chains. Moreover, taking advantage nanogaps fabric, authors demonstrated ability act net. Following deposition onto polymer-supported membrane, capable slowing down passage size-selective manner, suggesting potential application nanofiltration biomimetic channels. methods6Liu Scholar,10Li generating entanglements Leigh’s approach, tessellation extension pre-woven process advantages controlling cross sequence orientation based blocks, improve predictability precision There lot room remaining explored realm2Stoddart nanotopology, exemplified very six billion prime defined mathematicians synthesized date. paramount importance enrich toolkit introducing more complexity molecules. breakthroughs11Leigh Scholar,12August team represent strategic innovations materials. We optimistic strategy—as twisting, folding, threading done before—will expand reach lay foundation establishment topology-property relationships, forge state-of-the-art applications real Our foray galaxy nanotopology just begun.