A triaxial supramolecular weave

Single crystals of purely organic free-standing two-dimensional woven polymer networks

The aesthetic and practicality of macroscopic fabrics continue to encourage chemists to weave molecules into interlaced patterns with the aim of providing emergent physical and chemical properties when compared with their starting materials. Weaving purely organic molecular threads into flawless two-dimensional patterns remains a formidable challenge, even though its feasibility has been proposed on several occasions. Herein we describe the synthesis of a flawless, purely organic, free-standing two-dimensional woven polymer network driven by dative B-N bonds. Single crystals of this woven polymer network were obtained and its well-defined woven topology was revealed by X-ray diffraction analysis. Free-standing two-dimensional monolayer nanosheets of the woven polymer network were exfoliated from the layered crystals using Scotch Magic Tape. The surface features of the nanosheets were investigated by integrated low-dose and cryogenic electron microscopy imaging techniques. These findings demonstrate the precise construction of purely organic woven polymer networks and highlight the unique opportunities for the application of woven topologies in two-dimensional organic materials.

Toward Molecular Textiles: Synthesis and Characterization of Molecular Patches

This works describes a new step into the assembly of molecular textiles by the use of covalent templating. To establish a well-founded base and to tackle pre-mature obstacles, expected during the fabrication of the desired 2D-material, we opted to investigate the in-solution synthesis of molecular patches e. g. cut-outs of a textile. A bi-functional cross-shaped monomer was designed, synthesized and was in-detail characterized by means of 1H-NMR and chiro-optical spectroscopy. In addition, x-ray structure crystallography was used to assess the absolute configuration. The monomer was used in an in-solution oligomerization to assemble the molecular patches via imine condensation, which revealed the formation of predominately dimeric patches. The imine-oligomer mixtures were further analyzed by reduction and cleaved to investigate the conditions required post mono-layer assembly. All reaction stages were followed by FT-IR and 1H-NMR analysis. Finally, we address the adsorption of the cross-shaped monomer onto a Au(111) surface, via high vacuum electrospray deposition. The subsequent annealing of the interface induced the on-surface imine condensation reaction, leading to unidimensional oligomers co-adsorbed with clusters of cyclic-dimers. Nc-AFM analysis revealed the tridimensional molecular structures, and together with electrospray deposition technique showed to be a promising pathway to investigate potential monomer candidates.

Diverse Proteomimetic Frameworks via Rational Design of π-Stacking Peptide Tectons

Peptide-based frameworks aim to integrate protein architecture into solid-state materials using simpler building blocks. Despite the growing number of peptide frameworks, there are few strategies to rationally engineer essential properties like pore size and shape. Designing peptide assemblies is generally hindered by the difficulty of predicting complex networks of weak intermolecular interactions. Peptides conjugated to polyaromatic groups are a unique case where assembly appears to be strongly driven by π-π interactions, suggesting that rationally adjusting the geometry of the π-stackers could create novel structures. Here, we report peptide elongation as a simple mechanism to predictably tune the angle between the π-stacking groups to produce a remarkable diversity of pore shapes and sizes, including some that are mesoporous. Notably, rapid jumps in pore size and shape can occur with just a single amino acid insertion. The geometry of the π-stacking residues also significantly influences framework structure, representing an additional dimension for tuning. Lastly, sequence identity can also indirectly modulate the π-π interactions. By correlating each of these factors with detailed crystallographic data, we find that, despite the complexity of peptide structure, the shape and polarity of the tectons are straightforward predictors of framework structure. These guidelines are expected to accelerate the development of advanced porous materials with protein-like capabilities.

Proline Analogues

Within the canonical repertoire of the amino acid involved in protein biogenesis, proline plays a unique role as an amino acid presenting a modified backbone rather than a side-chain. Chemical structures that mimic proline but introduce changes into its specific molecular features are defined as proline analogues. This review article summarizes the existing chemical, physicochemical, and biochemical knowledge about this peculiar family of structures. We group proline analogues from the following compounds: substituted prolines, unsaturated and fused structures, ring size homologues, heterocyclic, e.g., pseudoproline, and bridged proline-resembling structures. We overview (1) the occurrence of proline analogues in nature and their chemical synthesis, (2) physicochemical properties including ring conformation and cis/trans amide isomerization, (3) use in commercial drugs such as nirmatrelvir recently approved against COVID-19, (4) peptide and protein synthesis involving proline analogues, (5) specific opportunities created in peptide engineering, and (6) cases of protein engineering with the analogues. The review aims to provide a summary to anyone interested in using proline analogues in systems ranging from specific biochemical setups to complex biological systems.

Epitaxially Grown Mechanically Robust 2D Thin Film of Secondary Interactions Led Molecularly Woven Material

Molecularly woven materials with striking mechanical resilience, and 2D controlled topologies like textiles, fishing nets, and baskets are highly anticipated. Molecular weaving exclusively apprehended by the secondary interactions expanding to laterally grown 2D self-assemblies with retained crystalline arrangement is stimulating. The interlacing entails planar molecules screwed together to form 2D woven thin films. Here, secondary interactions led 2D interlaced molecularly woven material (2°MW) built by 1D helical threads of organic chromophores twisted together via end-to-end CH···O connections, held strongly at inter-crossing by multiple OH···N interactions to prevent slippage is presented. Whereas, 1D helical threads with face-to-face O-H···O connections sans interlacing led the non-woven material (2°NW). The polarity-driven directionality in 2°MW led the water-actuated epitaxial growth of 2D-sheets to lateral thin films restricted to nano-scale thickness. The molecularly woven thin film is self-healing, flexible, and mechanically resilient in nature, while maintaining the crystalline regularity is attributed to the supple secondary interactions (2°).

Folk arts-inspired twice-coagulated configuration-editable tough aerogels enabled by transformable gel precursors

Aerogels, as famous lightweight and porous nanomaterials, have attracted considerable attention in various emerging fields in recent decades, however, both low density and weak mechanical performance make their configuration-editing capability challenging. Inspired by folk arts, herein we establish a highly efficient twice-coagulated (TC) strategy to fabricate configuration-editable tough aerogels enabled by transformable gel precursors. As a proof of concept, aramid nanofibers (ANFs) and polyvinyl alcohol (PVA) are selected as the main components of aerogel, among which PVA forms a flexible configuration-editing gel network in the first coagulation process, and ANF forms a configuration-locking gel network in the second coagulation process. TC strategy guarantees the resulting aerogels with both high toughness and feasible configuration editing capability individually or simultaneously. Altogether, the resulting tough aerogels with special configuration through soft to hard modulation provide great opportunities to break through the performance limits of the aerogels and expand application areas of aerogels.

Directing Molecular Weaving of Covalent Organic Frameworks and Their Dimensionality by Angular Control

Although reticular chemistry has commonly utilized mutually embracing tetrahedral metal complexes as crossing points to generate three-dimensional molecularly woven structures, weaving in two dimensions remains largely unexplored. We report a new strategy to access 2D woven COFs by controlling the angle of the usually linear linker, resulting in the successful synthesis of a 2D woven pattern based on chain-link fence. The synthesis was accomplished by linking aldehyde-functionalized copper(I) bisphenanthroline complexes with bent 4,4'-oxydianiline building units. This results in the formation of a crystalline solid, termed COF-523-Cu, whose structure was characterized by spectroscopic techniques and electron and X-ray diffraction techniques to reveal a molecularly woven, twofold-interpenetrated chain-link fence. The present work significantly advances the concept of molecular weaving and its practice in the design of complex chemical structures.

Noncovalent Peptide Assembly Enables Crystalline, Permutable, and Reactive Thiol Frameworks

Though thiols are exceptionally versatile, their high reactivity has also hindered the synthesis and characterization of well-defined thiol-containing porous materials. Leveraging the mild conditions of the noncovalent peptide assembly, we readily synthesized and characterized a number of frameworks with thiols displayed at many unique positions and in several permutations. Importantly, nearly all assemblies were structurally determined using single-crystal X-ray diffraction to reveal their rich sequence-structure landscape and the cooperative noncovalent interactions underlying their assembly. These observations and supporting molecular dynamics calculations enabled rational engineering by the positive and negative design of noncovalent interactions. Furthermore, the thiol-containing frameworks undergo diverse single-crystal-to-single-crystal reactions, including toxic metal ion coordination (e.g., Cd2+, Pb2+, and Hg2+), selective uptake of Hg2+ ions, and redox transformations. Notably, we find a framework that supports thiol-nitrosothiol interconversion, which is applicable for biocompatible nitric oxide delivery. The modularity, ease of synthesis, functionality, and well-defined nature of these peptide-based thiol frameworks are expected to accelerate the design of complex materials with reactive active sites.

Formation of polyrotaxane crystals driven by dative boron-nitrogen bonds

The integration of mechanically interlocked molecules (MIMs) into purely organic crystalline materials is expected to produce materials with properties that are not accessible using more classic approaches. To date, this integration has proved elusive. We present a dative boron-nitrogen bond-driven self-assembly strategy that allows for the preparation of polyrotaxane crystals. The polyrotaxane nature of the crystalline material was confirmed by both single-crystal x-ray diffraction analysis and cryogenic high-resolution low-dose transmission electron microscopy. Enhanced softness and greater elasticity are seen for the polyrotaxane crystals than for nonrotaxane polymer controls. This finding is rationalized in terms of the synergetic microscopic motion of the rotaxane subunits. The present work thus highlights the benefits of integrating MIMs into crystalline materials.

Woven, Polycatenated, or Cage Structures: Effect of Modulation of Ligand Curvature in Heteroleptic Uranyl Ion Complexes

Combining the flexible zwitterionic dicarboxylate 4,4'-bis(2-carboxylatoethyl)-4,4'-bipyridinium (L) and the anionic dicarboxylate ligands isophthalate (ipht^2-) and 1,2-, 1,3-, or 1,4-phenylenediacetate (1,2-, 1,3-, and 1,4-pda^2-), of varying shape and curvature, has allowed isolation of five uranyl ion complexes by synthesis under solvo-hydrothermal conditions. [(UO₂)₂(L)(ipht)₂] (1) and [(UO₂)₂(L)(1,2-pda)₂]·2H₂O (2) have the same stoichiometry, and both crystallize as monoperiodic coordination polymers containing two uranyl-(anionic carboxylate) strands united by L linkers into a wide ribbon, all ligands being in the divergent conformation. Complex 3, [(UO₂)₂(L)(1,3-pda)₂]·0.5CH₃CN, with the same stoichiometry but ligands in a convergent conformation, is a discrete, binuclear species which is the first example of a heteroleptic uranyl carboxylate coordination cage. With all ligands in a divergent conformation, [(UO₂)₂(L)(1,4-pda)(1,4-pdaH)₂] (4) crystallizes as a sinuous and thread-like monoperiodic polymer; two families of chains run along different directions and are woven into diperiodic layers. Modification of the synthetic conditions leads to [(UO₂)₄(LH)₂(1,4-pda)₅]·H₂O·2CH₃CN (5), a monoperiodic polymer based on tetranuclear (UO₂)₄(1,4-pda)₄ rings; intrachain hydrogen bonding of the terminal LH⁺ ligands results in diperiodic network formation through parallel polycatenation involving the tetranuclear rings and the LH⁺ rods. Complexes 1-3 and 5 are emissive, with complex 2 having the highest photoluminescence quantum yield (19%), and their spectra show the maxima positions usual for tris-κ²O,O'-chelated uranyl cations.

Woven Polymer Networks: From Crystalline to Elastomeric Materials

Weaving technology has been extensively used for manufacturing macroscopic fabrics and satisfying the artistic demands of humans through the ages. Integrating woven geometries into molecular structures is a persistent pursuit, and yet a significant challenge to chemists, owing to the lack of effective methodologies to guide the regular mutual interlacing of molecular strands. In this Concept article, recent progress and related strategies in constructing woven polymer networks (WPNs) are summarized and discussed. An outlook is then given to highlight the future opportunities and challenges in the development of both molecularly woven structures and molecularly woven functional materials.

Cyanine Dye Coupling Mediates Self-assembly of a pH Sensitive Peptide into Novel 3D Architectures

Synthetic multichromophore systems are of great importance in artificial light harvesting devices, organic optoelectronics, tumor imaging and therapy. Here, we introduce a promising strategy for the construction of self-assembled peptide templated dye stacks based on coupling of a de novo designed pH sensitive peptide with a cyanine dye Cy5 at its N-terminus. Microscopic techniques, in particular cryogenic TEM (cryo-TEM) and cryo-electron tomography technique (cryo-ET), reveal two types of highly ordered three-dimensional assembly structures on the micrometer scale. Unbranched compact layered rods are observed at pH 7.4 and two-dimensional membrane-like assemblies at pH 3.4, both species displaying spectral features of H-aggregates. Molecular dynamics simulations reveal that the coupling of Cy5 moieties promotes the formation of both ultrastructures, whereas the protonation states of acidic and basic amino acid side chains dictates their ultimate three-dimensional organization.

Directing the Self-Assembly of Aromatic Foldamer Helices using Acridine Appendages and Metal Coordination

Folded molecules provide complex interaction interfaces amenable to sophisticated self-assembly motifs. Because of their high conformational stability, aromatic foldamers constitute suitable candidates for the rational elaboration of self-assembled architectures. Several multiturn helical aromatic oligoamides have been synthesized that possess arrays of acridine appendages pointing in one or two directions. The acridine units were shown to direct self-assembly in the solid state via aromatic stacking leading to recurrent helix-helix association patterns under the form of discrete dimers or extended arrays. In the presence of Pd(II), metal coordination of the acridine units overwhelms other forces and generates new metal-mediated multihelical self-assemblies, including macrocycles. These observations demonstrate simple access to different types of foldamer-containing architectures, ranging from discrete objects to 1D and, by extension, 2D and 3D arrays.

Knotting matters: orderly molecular entanglements

Entangling strands in a well-ordered manner can produce useful effects, from shoelaces and fishing nets to brown paper packages tied up with strings. At the nanoscale, non-crystalline polymer chains of sufficient length and flexibility randomly form tangled mixtures containing open knots of different sizes, shapes and complexity. However, discrete molecular knots of precise topology can also be obtained by controlling the number, sequence and stereochemistry of strand crossings: orderly molecular entanglements. During the last decade, substantial progress in the nascent field of molecular nanotopology has been made, with general synthetic strategies and new knotting motifs introduced, along with insights into the properties and functions of ordered tangle sequences. Conformational restrictions imparted by knotting can induce allostery, strong and selective anion binding, catalytic activity, lead to effective chiral expression across length scales, binding modes in conformations efficacious for drug delivery, and facilitate mechanical function at the molecular level. As complex molecular topologies become increasingly synthetically accessible they have the potential to play a significant role in molecular and materials design strategies. We highlight particular examples of molecular knots to illustrate why these are a few of our favourite things.

A Peptide Nanocage Constructed by Self-Assembly of Oligoproline Conjugates

Cage-like supramolecular assemblies called molecular cages, which possess attractive functions, have been prepared. Although biomolecule-based nanocages are required for biological/medical applications such as drug delivery systems, the majority of nanocages are constructed using aromatic compounds with lower biocompatibility and biodegradability. In this study, the construction of a peptide nanocage consisting of an oligoproline conjugate is demonstrated. The conjugate was easy to prepare and had high biocompatibility. The oligoproline moiety of the conjugate had a rigid, rod-like structure suitable for the backbone of the supramolecular nanocage. The conjugates self-assembled to form peptide nanocages with a huge inner cavity.

Shape-assisted self-assembly

Self-assembly and molecular recognition are critical processes both in life and material sciences. They usually depend on strong, directional non-covalent interactions to gain specificity and to make long-range organization possible. Most supramolecular constructs are also at least partially governed by topography, whose role is hard to disentangle. This makes it nearly impossible to discern the potential of shape and motion in the creation of complexity. Here, we demonstrate that long-range order in supramolecular constructs can be assisted by the topography of the individual units even in the absence of highly directional interactions. Molecular units of remarkable simplicity self-assemble in solution to give single-molecule thin two-dimensional supramolecular polymers of defined boundaries. This dramatic example spotlights the critical function that topography can have in molecular assembly and paves the path to rationally designed systems of increasing sophistication.

Self-assembly and molecular recognition usually depend on strong, directional non-covalent interactions but also topography can play a role in the formation of supramolecular constructs which makes it nearly impossible to discern the potential of shape and motion in the creation of complexity. Here, the authors demonstrate that long-range order in supramolecular constructs can be assisted by the topography of the individual units even in the absence of highly directional interactions.

Assembly of π-Stacking Helical Peptides into a Porous and Multivariable Proteomimetic Framework

The evolution of proteins from simpler, self-assembled peptides provides a powerful blueprint for the design of complex synthetic materials. Previously, peptide-metal frameworks using short sequences (≤3 residues) have shown great promise as proteomimetic materials that exhibit sophisticated capabilities. However, their development has been hindered due to few variable residues and restricted choice of side-chains that are compatible with metal ions. Herein, we developed a noncovalent strategy featuring π-stacking bipyridyl residues to assemble much longer peptides into crystalline frameworks that tolerate even previously incompatible acidic and basic functionalities and allow an unprecedented level of pore variations. Single-crystal X-ray structures are provided for all variants to guide and validate rational design. These materials exhibit hallmark proteomimetic behaviors such as guest-selective induced fit and assembly of multimetallic units. Significantly, we demonstrate facile optimization of the framework design to substantially increase affinity toward a complex organic molecule.

Bottom-up supramolecular assembly in two dimensions

The self-assembly of molecules in two dimensions (2D) is gathering attention from all disciplines across the chemical sciences. Attracted by the interesting properties of two-dimensional inorganic analogues, monomers of different chemical natures are being explored for the assembly of dynamic 2D systems. Although many important discoveries have been already achieved, great challenges are still to be addressed in this field. Hierarchical multicomponent assembly, directional non-covalent growth and internal structural control are a just a few of the examples that will be discussed in this perspective about the exciting present and the bright future of two-dimensional supramolecular assemblies.

The self-assembly of molecules in two dimensions (2D) is gathering attention from all disciplines across the chemical sciences. This perspective discusses the main strategies to direct the supramolecular self-assembly of organic monomers in 2D.

Vernier template synthesis of molecular knots

Molecular knots are often prepared using metal helicates to cross the strands. We found that coordinatively mismatching oligodentate ligands and metal ions provides a more effective way to synthesize larger knots using Vernier templating. Strands composed of different numbers of tridentate 2,6-pyridinedicarboxamide groups fold around nine-coordinate lanthanide (III) ions to generate strand-entangled complexes with the lowest common multiple of coordination sites for the ligand strands and metal ions. Ring-closing olefin metathesis then completes the knots. A 3:2 (ditopic strand:metal) Vernier assembly produces +3₁#+3₁ and -3₁#-3₁ granny knots. Vernier complexes of 3:4 (tetratopic strand:metal) stoichiometry selectively form a 378-atom-long trefoil-of-trefoils triskelion knot with 12 alternating strand crossings or, by using opposing stereochemistry at the terminus of the strand, an inverted-core triskelion knot with six alternating and six nonalternating strand crossings.

Molecular weaving

Historically, the interlacing of strands at the molecular level has mainly been limited to coordination polymers and DNA. Despite being proposed on a number of occasions, the direct, bottom-up assembly of molecular building blocks into woven organic polymers remained an aspirational, but elusive, target for several decades. However, recent successes in two-dimensional and three-dimensional molecular-level weaving now offer new opportunities and research directions at the interface of polymer science and molecular nanotopology. This Perspective provides an overview of the features and potential of the periodic nanoscale weaving of polymer chains, distinguishing it from randomly entangled polymer networks and rigid crystalline frameworks. We review the background and experimental progress so far, and conclude by considering the potential of molecular weaving and outline some of the current and future challenges in this emerging field.

Smooth Triaxial Weaving with Naturally Curved Ribbons

Triaxial weaving is a handicraft technique that has long been used to create curved structures using initially straight and flat ribbons. Weavers typically introduce discrete topological defects to produce nonzero Gaussian curvature, albeit with faceted surfaces. We demonstrate that, by tuning the in-plane curvature of the ribbons, the integrated Gaussian curvature of the weave can be varied continuously, which is not feasible using traditional techniques. Further, we reveal that the shape of the physical unit cells is dictated solely by the in-plane geometry of the ribbons, not elasticity. Finally, we leverage the geometry-driven nature of triaxial weaving to design a set of ribbon profiles to weave smooth spherical, ellipsoidal, and toroidal structures.

On Borromean links and related structures

The creation of knotted, woven and linked molecular structures is an exciting and growing field in synthetic chemistry. Presented here is a description of an extended family of structures related to the classical `Borromean rings', in which no two rings are directly linked. These structures may serve as templates for the designed synthesis of Borromean polycatenanes. Links of n components in which no two are directly linked are termed `n-Borromean' [Liang & Mislow (1994). J. Math. Chem. 16, 27-35]. In the classic Borromean rings the components are three rings (closed loops). More generally, they may be a finite number of periodic objects such as graphs (nets), or sets of strings related by translations as in periodic chain mail. It has been shown [Chamberland & Herman (2015). Math. Intelligencer, 37, 20-25] that the linking patterns can be described by complete directed graphs (known as tournaments) and those up to 13 vertices that are vertex-transitive are enumerated. In turn, these lead to ring-transitive (isonemal) n-Borromean rings. Optimal piecewise-linear embeddings of such structures are given in their highest-symmetry point groups. In particular, isonemal embeddings with rotoinversion symmetry are described for three, five, six, seven, nine, ten, 11, 13 and 14 rings. Piecewise-linear embeddings are also given of isonemal 1- and 2-periodic polycatenanes (chains and chain mail) in their highest-symmetry setting. Also the linking of n-Borromean sets of interleaved honeycomb nets is described.

Electroactive peptide-based supramolecular polymers

The electroactivity as a supramolecular feature of intelligently designed self-assembled systems stimulates a wide interest in development of new stimuli-responsive biomaterials. A diverse set of nanostructures are fabricated through programmed self-assembly of molecules for functional materials. Electroactive groups are conjugated as a functional moiety for organic semiconductor applications. In this review, we present recent examples of self-assembling peptide molecules and electroactive units for supramolecular functional electronic ​and optical materials with potential biomedical and bioelectronics applications.

Peptide-Protein Interactions: From Drug Design to Supramolecular Biomaterials

The self-recognition and self-assembly of biomolecules are spontaneous processes that occur in Nature and allow the formation of ordered structures, at the nanoscale or even at the macroscale, under thermodynamic and kinetic equilibrium as a consequence of specific and local interactions. In particular, peptides and peptidomimetics play an elected role, as they may allow a rational approach to elucidate biological mechanisms to develop new drugs, biomaterials, catalysts, or semiconductors. The forces that rule self-recognition and self-assembly processes are weak interactions, such as hydrogen bonding, electrostatic attractions, and van der Waals forces, and they underlie the formation of the secondary structure (e.g., α-helix, β-sheet, polyproline II helix), which plays a key role in all biological processes. Here, we present recent and significant examples whereby design was successfully applied to attain the desired structural motifs toward function. These studies are important to understand the main interactions ruling the biological processes and the onset of many pathologies. The types of secondary structure adopted by peptides during self-assembly have a fundamental importance not only on the type of nano- or macro-structure formed but also on the properties of biomaterials, such as the types of interaction, encapsulation, non-covalent interaction, or covalent interaction, which are ultimately useful for applications in drug delivery.

A molecular endless (74) knot

Current strategies for the synthesis of molecular knots focus on twisting, folding and/or threading molecular building blocks. Here we report that Zn(II) or Fe(II) ions can be used to weave ligand strands to form a woven 3 × 3 molecular grid. We found that the process requires tetrafluoroborate anions to template the assembly of the interwoven grid by binding within the square cavities formed between the metal-coordinated criss-crossed ligands. The strand ends of the grid can subsequently be joined through within-grid alkene metathesis reactions to form a topologically trivial macrocycle (unknot), a doubly interlocked [2]catenane (Solomon link) and a knot with seven crossings in a 258-atom-long closed loop. This 7₄ knot topology corresponds to that of an endless knot, which is a basic motif of Celtic interlace, the smallest Chinese knot and one of the eight auspicious symbols of Buddhism and Hinduism. The weaving of molecular strands within a discrete layer by anion-template metal-ion coordination opens the way for the synthesis of other molecular knot topologies and to woven polymer materials.

Peptide-Metal Frameworks with Metal Strings Guided by Dispersion Interactions

Despite impressive advances in the construction of metal-organic frameworks (MOFs), the formation of networks from peptidic ligands is difficult, though they are sought after for their modularity and biocompatibility. Herein we present a peptide-metal framework that consists of helical oligoproline ligands and Zn/K (or Zn/Rb). The crystalline network contains pleated nanosheets with the metal ions aligned in strings. This unprecedented architecture derives from under-appreciated London dispersion interactions between the oligoproline ligands that play in concert with the metal coordination to create the network. Hence, the secondary structure of the peptidic ligand represents an additional control element for the creation of new MOF architectures. We anticipate that our results will instruct the design of further peptidic MOFs and enable the generation of versatile biocompatible materials.

Self-assembly of a layered two-dimensional molecularly woven fabric

Fabrics-materials consisting of layers of woven fibres-are some of the most important materials in everyday life¹. Previous nanoscale weaves^2-16 include isotropic crystalline covalent organic frameworks^12-14 that feature rigid helical strands interlaced in all three dimensions, rather than the two-dimensional^17,18 layers of flexible woven strands that give conventional textiles their characteristic flexibility, thinness, anisotropic strength and porosity. A supramolecular two-dimensional kagome weave¹⁵ and a single-layer, surface-supported, interwoven two-dimensional polymer¹⁶ have also been reported. The direct, bottom-up assembly of molecular building blocks into linear organic polymer chains woven in two dimensions has been proposed on a number of occasions^19-23, but has not previously been achieved. Here we demonstrate that by using an anion and metal ion template, woven molecular 'tiles' can be tessellated into a material consisting of alternating aliphatic and aromatic segmented polymer strands, interwoven within discrete layers. Connections between slowly precipitating pre-woven grids, followed by the removal of the ion template, result in a wholly organic molecular material that forms as stacks and clusters of thin sheets-each sheet up to hundreds of micrometres long and wide but only about four nanometres thick-in which warp and weft single-chain polymer strands remain associated through periodic mechanical entanglements within each sheet. Atomic force microscopy and scanning electron microscopy show clusters and, occasionally, isolated individual sheets that, following demetallation, have slid apart from others with which they were stacked during the tessellation and polymerization process. The layered two-dimensional molecularly woven material has long-range order, is birefringent, is twice as stiff as the constituent linear polymer, and delaminates and tears along well-defined lines in the manner of a macroscopic textile. When incorporated into a polymer-supported membrane, it acts as a net, slowing the passage of large ions while letting smaller ions through.

Conformation and Morphology of 4-(NH2/OH)-Substituted l/d-Prolyl Polypeptides: Effect of Homo- and Heterochiral Backbones on Formation of β-Structures and Nanofibers

The relative stereochemistry of C2 and C4 in 4-substituted prolyl polypeptides plays an important role in defining the derived conformation in solution. cis-(2S,4S)-Amino/hydroxy-l-prolyl polypeptide (lC-Amp 9/lC-Hyp 9) shows a PPII conformation in phosphate buffer and a β-structure in a relatively hydrophobic solvent, trifluoroethanol (TFE). It is now demonstrated that the homochiral enantiomeric cis-substituted d-prolyl polypeptide (dC-Amp 9/dC-Hyp 9) exhibits mirror image β-structures in TFE. In the case of alternating heterochiral prolyl peptides, it is the trans-substituted [lT(2S,4R)-dT(2R,4S)] n prolyl polypeptide that shows β-structures in TFE, while the cis-substituted [lC(2S,4S)-dC(2R,4R)] n prolyl polypeptide is disordered in both phosphate buffer and TFE. The results highlight the important chirality-specific structural requirements for β-structure formation. The observed conformation in solution (circular dichroism (CD)) is also correlated with the morphology of the self-assemblies (field emission scanning electron microscopy (FESEM)), with the PPII form leading to spherical nanoparticles and β-structures leading to nanofiber formation. The results shed light on the role of relative stereochemistry at C2 and C4 in defining the polyproline peptide conformation in solution and how different conformations drive self-assemblies of peptides toward specific nanostructures.

Chiral cyclic [n]spirobifluorenylenes: carbon nanorings consisting of helically arranged quaterphenyl rods illustrating partial units of woven patterns

Chiral cyclic [n]spirobifluorenylenes consisting of helically arranged quaterphenyl rods, illustrating partial units of woven patterns, were designed and synthesized as a new family of carbon nanorings. The synthesis was accomplished by the Ni(0)-mediated Yamamoto-coupling of chiral spirobifluorene building blocks. The structures of the cyclic 3-, 4-, and 5-mers were determined by X-ray crystallographic analysis. These carbon nanorings exhibited a strong violet colored emission with high quantum yields in solution (95%, 93%, and 94% for 3-, 4-, and 5-mer, respectively). Other spectroscopic properties, including their chiroptical properties, were also investigated. The g-values for circularly polarized luminescence were found to be in the order of 10⁻³. Characteristic spiroconjugation induced by multiple (≧3) bifluorenyl units, for example the even-odd effect of the number of units in the matching of the signs of the orbitals, was also indicated by DFT calculations.

Chiral cyclic [n]spirobifluorenylenes consisting of helically arranged quaterphenyl rods, illustrating partial units of woven patterns, were designed and synthesized as a new family of carbon nanorings.

Woven Polymer Networks via the Topological Transformation of a [2]Catenane

Weaving technology has been widely used to manufacture macroscopic fabrics to meet the artistic and practical needs of humanity for thousands of years. However, the fabrication of molecular fabrics with fascinating topologies and unique mechanical properties represents a significant challenge. Herein, we describe a topological transformation strategy to construct woven polymer networks (WPNs) at the molecular level via ring-opening metathesis polymerization (ROMP) of a zinc-template [2]catenane. The key feature of this approach is the exploitation of the pre-existing catenane crossing points that maintain the dense woven structure and the flexible alkyl chains on the [2]catenane that synergistically work with the crossing points to modulate the physicochemical and mechanical properties of the woven materials. As a result, the WPN possesses a certain degree of flexibility and stretchability, as well as high thermostability and mechanical robustness. Furthermore, we could remove the zinc ions to endow the WPN with more degrees of freedom and then enhance its mechanical behaviors by remetalation. This study not only provides a novel strategy toward woven materials with intriguing structural features and emergent mechanical adaptivities, but also highlights that mechanically interlocked molecules could offer unique opportunities for the construction of smart supramolecular materials with peculiar interlaced topologies at the molecular scale.

Patterning Porous Networks through Self-Assembly of Programmed Biomacromolecules

Two-dimensional (2D) porous networks are of great interest for the fabrication of complex organized functional materials for potential applications in nanotechnologies and nanoelectronics. This review aims at providing an overview of bottom-up approaches towards the engineering of 2D porous networks by using biomacromolecules, with a particular focus on nucleic acids and proteins. The first part illustrates how the advancements in DNA nanotechnology allowed for the attainment of complex ordered porous two-dimensional DNA nanostructures, thanks to a biomimetic approach based on DNA molecules self-assembly through specific hydrogen-bond base pairing. The second part focuses the attention on how polypeptides and proteins structural properties could be used to engineer organized networks templating the formation of multifunctional materials. The structural organization of all examples is discussed as revealed by scanning probe microscopy or transmission electron microscopy imaging techniques.

Ligand Mediated Metal Cations Exchanges within Metallo-Dynameric Solid Films

Dynameric solid films may be generated via the adequate imine-bond connection between bis(pyridine-2,6-diimine) core centres, coordinated with different metal cations and diaminoPEG connectors. The adequate selection of metal cations leads to cross-linked metallo-dynameric films, allowing the fine modulation of their colour and mechanical property. The coordination of the metal cations and bis(pyridine-2,6-diimine), results in the formation of interlocked structures, leading to the most probably formation of interweaved structures with better mechanical properties than those formed in the absence of the metallic cations. Removal and addition of metal cations from solid films can be achieved via tris(2-aminoethyl)amine (TREN) complexing agent, which strongly binds the metal cations, followed by subsequent insertion of other metallic cations. It allows a ligand-modulated dynamic release of the metal cations from the solid films, together with colour transfer and change of mechanical strength at the interfaces between various solid films.

Graphene Quantum Dots in the Game of Directing Polymer Self-Assembly to Exotic Kagome Lattice and Janus Nanostructures

Graphene quantum dots (GQDs) are the harbingers of a paradigm shift that revitalize self-assembly of the colloidal puzzle by adding shape and size to the material-design palette. Although self-assembly is ubiquitous in nature, the extent to which these molecular legos can be engineered reminds us that we are still apprenticing polymer carpenters. In this quest to unlock exotic nanostructures ascending from eventual anisotropy, we have utilized different concentrations of GQDs as a filler in free-radical-mediated aqueous copolymerization. Extensive polymer grafting over the geometrically confined landscape of GQDs (0.05%) bolsters crystallization instilling a loom which steers interaction of polymeric cilia into interlaced equilateral triangles with high sophistication. Such two-dimensional (2D) assemblies epitomizing the planar tiling of "Star of David" forming a molecular kagome lattice (KL) without metal templation evoke petrichor. Interestingly, a higher percentage (0.3%) of GQDs allow selective tuning of the interfacial property of copolymers breaking symmetry due to surface energy incongruity, producing exotic Janus nanomicelles (JNMs). Herein, with the help of a suite of characterizations, we delineate the mechanism behind the formation of the KL and JNMs which forms a depot of heightened drug accretion with targeted delivery of 5-fluorouracil in the colon as validated by gamma scintigraphy studies.

Orthogonal Halogen-Bonding-Driven 3D Supramolecular Assembly of Right-Handed Synthetic Helical Peptides

Peptide-mediated self-assembly is a prevalent method for creating highly ordered supramolecular architectures. Herein, we report the first example of orthogonal C-X⋅⋅⋅X-C/C-X⋅⋅⋅π halogen bonding and hydrogen bonding driven crystalline architectures based on synthetic helical peptides bearing hybrids of l-sulfono-γ-AApeptides and natural amino acids. The combination of halogen bonding, intra-/intermolecular hydrogen bonding, and intermolecular hydrophobic interactions enabled novel 3D supramolecular assembly. The orthogonal halogen bonding in the supramolecular architecture exerts a novel mechanism for the self-assembly of synthetic peptide foldamers and gives new insights into molecular recognition, supramolecular design, and rational design of biomimetic structures.

Oligoprolines guide the self-assembly of quaterthiophenes

Control over the molecular organization of π-conjugated oligothiophenes into different types of supramolecular assemblies is key to their use in organic electronics but difficult to achieve as these chromophores have a pronounced tendency to aggregate. Herein we show that oligoprolines, which do not self-assemble on their own, control the self-assembly of quaterthiophenes. Spectroscopic, microscopic, and diffraction studies with quaterthiophene-oligoproline conjugates revealed the formation of mono- or double-layered sheets or, alternatively, helically twisted ribbons - depending on the length of the oligoproline. The dimensions of the nanoscopic objects, which extend into the micrometer regime, correlate with the molecular dimensions of the quaterthiophene-oligoproline building blocks.