Structural Diversity in the Self‐Assembly of Pseudopeptidic Macrocycles

The self‐assembling abilities of several pseudopeptidic macrocycles have been thoroughly studied both in the solid (SEM, TEM, FTIR) and in solution (NMR, UV, CD, FTIR) states. Detailed microscopy revealed large differences in the morphology of the self‐assembling micro/nanostructures depending on the macrocyclic chemical structures. Self‐assembly was triggered by the presence of additional methylene groups or by changing from para to meta geometry of the aromatic phenylene backbone moiety. More interestingly, the nature of the side chain also plays a fundamental role in some of the obtained nanostructures, thus producing structures from long fibers to hollow spheres. These nanostructures were obtained in different solvents and on different surfaces, thus implying that the chemical information for the self‐assembly is contained in the molecular structure. Dilution NMR studies (chemical shift and self‐diffusion rates) suggest the formation of incipient aggregates in solution by a combination of hydrogen‐bonding and π–π interactions, thus implicating amide and aryl groups, respectively. Electronic spectroscopy further supports the π–π interactions because the compounds that lead to fibers show large hypochromic shifts in the UV spectra. Moreover, the fiber‐forming macrocycles also showed a more intense CD signature. The hydrogen‐bonding interactions within the nanostructures were also characterized by attenuated total‐reflectance FTIR spectroscopy, which allowed us to monitor the complete transition from the solution to the dried nanostructure. Overall, we concluded that the self‐assembly of this family of pseudopeptidic macrocycles is dictated by a synergic action of hydrogen‐bonding and π–π interactions. The feasibility and geometrical disposition of these interactions finally render a hierarchical organization, which has been rationalized with a proposal of a model. The understanding of the process at the molecular level has allowed us to prepare hybrid soft materials.     

Multicomponent Supramolecular Systems: Self‐Organization in Coordination‐Driven Self‐Assembly

The self‐organization of multicomponent supramolecular systems involving a variety of two‐dimensional (2 D) polygons and three‐dimensional (3 D) cages is presented. Nine self‐organizing systems, SS₁ – SS₉ , have been studied. Each involves the simultaneous mixing of organoplatinum acceptors and pyridyl donors of varying geometry and their selective self‐assembly into three to four specific 2 D (rectangular, triangular, and rhomboid) and/or 3 D (triangular prism and distorted and nondistorted trigonal bipyramidal) supramolecules. The formation of these discrete structures is characterized using NMR spectroscopy and electrospray ionization mass spectrometry (ESI‐MS). In all cases, the self‐organization process is directed by: 1) the geometric information encoded within the molecular subunits and 2) a thermodynamically driven dynamic self‐correction process. The result is the selective self‐assembly of multiple discrete products from a randomly formed complex. The influence of key experimental variables ‐ temperature and solvent ‐ on the self‐correction process and the fidelity of the resulting self‐organization systems is also described.     

One‐Pot Mechanosynthesis with Three Levels of Molecular Self‐Assembly: Coordination Bonds,Hydrogen Bonds and Host–Guest Inclusion

Liquid‐assisted grinding (LAG) was used to combine three levels of molecular self‐assembly into a one‐pot mechanochemical approach for the construction of metal–organic materials. The approach was applied for the construction of three adducts of cobalt(II) dibenzoylmethanate with isonicotinamide, nicotinamide and imidazole, to screen for their inclusion compounds. The one‐pot process consists of: i) The coordination‐driven binding of addends to the equatorially‐protected metal ion, resulting in “wheel‐and‐axle”‐shaped complexes; ii) self‐assembly of resulting complexes by way of hydrogen‐bonded synthons to form metal–organic inclusion hosts; iii) in situ inclusion of the grinding liquid in the resulting host. This approach provided quantitatively and within 20 min the known inclusion compounds of the bis(isonicotinamide) adduct in a single synthetic step. Changing the liquid phase in LAG was used to explore the inclusion behaviour of new wheel‐and‐axle adducts with nicotinamide and imidazole, revealing several inclusion compounds, as well as two polymorphs, of the bis(nicotinamide) host. Preliminary results suggest that one‐pot LAG is superior to solution synthesis in screening for metal–organic inclusion compounds. The difference between the methods is rationalised in terms of reactant solubility and solvent competition. In contrast to the nicotinamide adduct, the bis(imidazole) adduct did not form inclusion compounds. The difference in the inclusion properties of the two adducts is rationalised by structural information gathered by single crystal and powder X‐ray diffraction.     

Hierarchical Self‐Assembly of Supramolecular Hydrophobic Metallacycles into Ordered Nanostructures

We describe herein the hierarchical self‐assembly of discrete supramolecular metallacycles into ordered fibers or spherical particles through multiple noncovalent interactions. A new series of well‐defined metallacycles decorated with long alkyl chains were obtained through metal–ligand interactions, which were capable of aggregating into ordered fibroid or spherical nanostructures on the surface, mostly driven by hydrophobic interactions. In‐depth studies indicated that the morphology diversity was originated from the structural information encoded in the metallacycles, including the number of alkyl chains and their spatial orientation. Interestingly, the morphology of the metallacycle aggregates could be tuned by changing the solvent polarity. These findings are of special significance since they provide a simple yet highly controllable approach to prepare ordered and tunable nanostructures from small building blocks by means of hierarchical self‐assembly.     

Synthesis and Supramolecular Self‐Assembly of Coil‐Rod‐Coil Molecules: The Relationship between Self‐Assembled Nanostructures and Molecular Structures

Herein, the relationship between the supramolecularly self‐assembled nanostructures and the chemical structures of coil‐rod‐coil molecules is discussed. A series of nonamphiphilic coil‐rod‐coil molecules with different alkyl chains, central mesogenic groups, and chemical linkers were designed and synthesized. The solvent‐mediated supramolecular self‐assembling of these coil‐rod‐coil molecules resulted in rolled‐up nanotubes, nanofibers, submicron sized belts, needle‐like microcrystals, and amorphous structures. The self‐assembling behaviors of these coil‐rod‐coil molecules have been systematically investigated to reveal the relationship between the supramolecularly self‐assembled nanostructures and their chemical structures. With respect to the formation of rolled‐up nanotubes by self‐assembly of coil‐rod‐coil molecules, we have systematically investigated the following three influencing structural factors: 1) the alkyl chain length; 2) the central mesogenic group; (3) the linker type. These studies disclosed the key structural features of coil‐rod‐coil molecules for the formation of rolled‐up nanotubes.     

Orthogonally Self‐Assembled Multifunctional Block Copolymers

We report the synthesis of telechelic poly(norbornene) and poly(cyclooctene) homopolymers by ring‐opening metathesis polymerization (ROMP) and their subsequent functionalization and block copolymer formation based on noncovalent interactions. Whereas all the poly(norbornene)s contain either a metal complex or a hydrogen‐bonding moiety along the polymer side‐chains, together with a single hydrogen‐bonding‐based molecular recognition moiety at one terminal end of the polymer chain. These homopolymers allow for the formation of side‐chain‐functionalized AB and ABA block copolymers through self‐assembly. The orthogonal natures of all side‐ and main‐chain self‐assembly events were demonstrated by ¹H NMR spectroscopy and isothermal titration calorimetry. The resulting fully functionalized block copolymers are the first copolymers combining both side‐ and main‐chain self‐assembly, thereby providing a high degree of control over copolymer functionalization and architecture and bringing synthetic materials one step closer to the dynamic self‐assembly structures found in nature.     

Engineering Hierarchical Nanostructures by Elastocapillary Self‐Assembly

Surfaces coated with nanoscale filaments such as silicon nanowires and carbon nanotubes are potentially compelling for high‐performance battery and capacitor electrodes, photovoltaics, electrical interconnects, substrates for engineered cell growth, dry adhesives, and other smart materials. However, many of these applications require a wet environment or involve wet processing during their synthesis. The capillary forces introduced by these wet environments can lead to undesirable aggregation of nanoscale filaments, but control of capillary forces can enable manipulation of the filaments into discrete aggregates and novel hierarchical structures. Recent studies suggest that the elastocapillary self‐assembly of nanofilaments can be a versatile and scalable means to build complex and robust surface architectures. To enable a wider understanding and use of elastocapillary self‐assembly as a fabrication technology, we give an overview of the underlying fundamentals and classify typical implementations and surface designs for nanowires, nanotubes, and nanopillars made from a wide variety of materials. Finally, we discuss exemplary applications and future opportunities to realize new engineered surfaces by the elastocapillary self‐assembly of nanofilaments.     

Allyl‐Functionalized Dioxynaphthalene[38]Crown‐10 Macrocycles: Synthesis,Self‐Assembly,and Thiol‐ene Functionalization

Five dioxynaphthalene[38]‐crown‐10 ( DNP38C10 ) macrocycles bearing one, two, three, or four allyl moieties have been synthesized and their ability to spontaneously self‐assemble with methyl viologen to form [2]pseudorotaxanes has been evaluated. Association constants between methyl viologen and several of the allyl‐functionalized DNP38C10 macrocycles are found to be comparable to that of methyl viologen and unfunctionalized DNP38C10 , however, the enthalpic and entropic factors that underlie overall binding free energy vary systematically with increasing allyl substitution. These variations are explained through a combination of solution phase and solid‐state analysis of the macrocycles and their complexes. The utility of endowing DNP38C10 macrocycles with allyl moieties is further demonstrated by the ease with which they can be functionalized through thiol‐ene click chemistry.     

Two‐Dimensional Nanoporous Networks Formed by Liquid‐to‐Solid Transfer of Hydrogen‐Bonded Macrocycles Built from DNA Bases

We present an approach that makes use of DNA base pairing to produce hydrogen‐bonded macrocycles whose supramolecular structure can be transferred from solution to a solid substrate. A hierarchical assembly process ultimately leads to two‐dimensional nanostructured porous networks that are able to host size‐complementary guests.     

Self‐Assembled Ultralong Chiral Nanotubes and Tuning of Their Chirality Through the Mixing of Enantiomeric Components

Enantiomeric L ‐ or D ‐glutamic acid based lipids were designed and their self‐assembly was investigated. It was found that at a certain concentration, either L ‐ or D ‐enantiomeric derivatives could self‐assemble in absolute alcohol to form a white organogel, which was composed of ultralong nanotubes with an aspect ratio higher than 1000. Further investigations revealed that these nanotubes were in chiral forms. The chirality of the nanotubes was determined by that of the enantiomers employed. In addition, when D and L enantiomers were mixed in different ratios, the nanotube could be tuned consecutively from nanotubes with a helical seam to nanotwists, the chirality of which being determined by the excess enantiomer in the mixed systems. In the case of an equimolar mixture of the enantiomers, flat nanoplates instead of helical nanotubes or nanotwists were obtained. The FTIR vibrational data and XRD layer‐distance values showed a consecutive change as a function of the enantiomeric excess. It was further revealed that the slightly stronger interaction between D –L enantiomeric pairs than that between D –D or L –L pairs was responsible for the formation of the diverse self‐assembled nanostructures.