Atomically Precise Nanocluster Assemblies Encapsulating Plasmonic Gold Nanorods

The self‐assembled structures of atomically precise, ligand‐protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs) is presented. Unlike highly sophisticated DNA nanotechnology, this strategically simple hydrogen bonding‐directed self‐assembly of nanoclusters leads to octahedral nanocrystals encapsulating GNRs. Specifically, the p‐mercaptobenzoic acid (pMBA)‐protected atomically precise silver nanocluster, Na₄[Ag₄₄(pMBA)₃₀], and pMBA‐functionalized GNRs were used. High‐resolution transmission and scanning transmission electron tomographic reconstructions suggest that the geometry of the GNR surface is responsible for directing the assembly of silver nanoclusters via H‐bonding, leading to octahedral symmetry. The use of water‐dispersible gold nanoclusters, Au_≈250(pMBA)_n and Au₁₀₂(pMBA)₄₄, also formed layered shells encapsulating GNRs. Such cluster assemblies on colloidal particles are a new category of precision hybrids with diverse possibilities.     

Template‐Free Synthesis of a Molecular Solomon Link by Two‐Component Self‐Assembly

A molecular Solomon link was synthesized in high yield through the template‐free, coordination‐driven self‐assembly of a carbazole‐functionalized donor and a tetracene‐based dinuclear ruthenium(II) acceptor. The doubly interlocked topology was realized by a strategically chosen ligand which was capable of participating in multiple CH ??? π and π–π interactions, as evidenced from single‐crystal X‐ray analysis and computational studies. This method is the first example of a two‐component self‐assembly of a molecular Solomon link using a directional bonding approach. The donor alone was not responsible for the construction of the Solomon link, and was confirmed by its noncatenane self‐assemblies obtained with other similar ruthenium(II) acceptors.     

Dynamic Self‐Assembly of Gold/Polymer Nanocomposites: pH‐Encoded Switching between 1D Nanowires and 3D Nanosponges

The design of tunable dynamic self‐assembly of nanoparticles with switchable assembled dimensions and morphologies is a challenging goal whose realization is vital for the evolution of smart nanomaterials. Herein, we report on chitosan polymer as an effective supramolecular “glue” for aldehyde‐modified Au nanoparticles to reversibly modulate the states of self‐assembled nanocomposites. By simultaneous integration of dynamic covalent Schiff base interactions and noncovalent hydrogen bonds, the chitosan/Au nanocomposites could reversibly transform their assembled morphologies from one‐dimensional nanowires to three‐dimensional nanosponges in response to the variation of pH value. Moreover, the obtained nanosponges could be used as an efficient pH‐controlled cargo release system.     

Supracolloidal Self‐Assembly of Divalent Janus 3D DNA Origami via Programmable Multivalent Host/Guest Interactions

We introduce divalent 3D DNA origami cuboids as truly monodisperse colloids and harness their ability for precision functionalization with defined patches and defined numbers of supramolecular binding motifs. We demonstrate that even adamantane/β‐cyclodextrin host/guest inclusion complexes of moderate association strength can induce efficient supracolloidal fibrillization at high dilution of the 3D DNA Origami as a result of cooperative multivalency. We show details on the assembly of Janus and non‐Janus 3D DNA origami into supracolloidal homo‐ and heterofibrils with respect to multivalency effects, electrostatic screening, and stoichiometry. We believe that the merger of 3D DNA origami with colloidal self‐assembly and supramolecular motifs provides new synergies at the interface of these disciplines to better understand multivalency effects, to promote structural complexity, and add non‐DNA assembling and switching mechanisms to DNA nanoscience.     

A Rationally Designed Thymidine‐Based Self‐Assembled Monolayer on a Gold Electrode for Electroanalytical Applications

A self‐assembled monolayer (SAM) of 1‐(3,5‐epidithio‐2,3,5‐trideoxy‐β‐d ‐threo‐pentofuranosyl)thymine (EFT) on a gold electrode was prepared and characterized by Raman spectral and electrochemical measurements. Voltammetric and electrochemical impedance measurements show that the SAM of EFT on a Au electrode impedes the electron‐transfer reaction. The SAM of EFT was successfully used for the voltammetric sensing of urate in neutral solution. The coexisting ascorbate anion does not interfere and therefore the EFT‐based electrode was able to quantify urate at the micromolar level in the presence of a large excess amount of ascorbate. To demonstrate the practical applications, the amount of urate in two different human serum samples was quantified by using the EFT‐based electrode; the results are in good agreement with those determined by the clinical method. DFT calculations show that both ascorbate and urate have noncovalent interactions including hydrogen‐bonding interactions with EFT.     

Supramolecular Self‐Assembly of Histidine‐Capped‐Dialkoxy‐Anthracene: A Visible‐Light‐Triggered Platform for Facile siRNA Delivery

Supramolecular self‐assembly of histidine‐capped‐dialkoxy‐anthracene (HDA) results in the formation of light‐responsive nanostructures. Single‐crystal X‐ray diffraction analysis of HDA shows two types of hydrogen bonding. The first hydrogen bond is established between the imidazole moieties while the second involves the oxygen atom of one amide group and the hydrogen atom of a second amide group. When protonated in acidic aqueous media, HDA successfully complexes siRNA yielding spherical nanostructures. This biocompatible platform controllably delivers siRNA with high efficacy upon visible‐light irradiation leading up to 90 % of gene silencing in live cells.     

Homochiral [2.2]Paracyclophane Self‐Assembly Promoted by Transannular Hydrogen Bonding

[2.2]paracyclophane (pCp), unlike many π‐building blocks, has been virtually unexplored in supramolecular constructs. Reported here is the synthesis and characterization of the first pCp derivatives capable of programmed self‐assembly into extended cofacial π‐stacks in solution and the solid state. The design employs transannular (intramolecular) hydrogen bonds (H‐bonds), hitherto unstudied in pCps, between pseudo‐ortho‐positioned amides of a pCp‐4,7,12,15‐tetracarboxamide (pCpTA) to preorganize the molecules for intermolecular H‐bonding with π‐stacked neighbors. X‐ray crystallography confirms the formation of homochiral, one‐dimensional pCpTA stacks helically laced with two H‐bond strands. The chiral sense is dictated by the planar chirality (R_p or S_p) of the pCpTA monomers. A combination of NMR, IR, and UV/Vis studies confirms the formation of the first supramolecular pCp polymers in solution.     

Herringbone and Helical Self‐Assembly of π‐Conjugated Molecules in the Solid State through CH/π Hydrogen Bonds

Self‐organization of organic molecules through weak noncovalent forces such as CH/π interactions and creation of large hierarchical supramolecular structures in the solid state are at the very early stage of research. The present study reports direct evidence for CH/π interaction driven hierarchical self‐assembly in π‐conjugated molecules based on custom‐designed oligophenylenevinylenes (OPVs) whose structures differ only in the number of carbon atoms in the tails. Single‐crystal X‐ray structures were resolved for these OPV synthons and the existence of long‐range multiple‐arm CH/π interactions was revealed in the crystal lattices. Alignment of these π‐conjugated OPVs in the solid state was found to be crucial in producing either right‐handed herringbone packing in the crystal or left‐handed helices in the liquid‐crystalline mesophase. Pitch‐ and roll‐angle displacements of OPV chromophores were determined to trace the effect of the molecular inclination on the ordering of hierarchical structures. Furthermore, circular dichroism studies on the OPVs were carried out in the aligned helical structures to prove the existence of molecular self‐assembly. Thus, the present strategy opens up new approaches in supramolecular chemistry based on weak CH/π hydrogen bonding, more specifically in π‐conjugated materials.     

Self‐Assembly of Proteins: Towards Supramolecular Materials

The study of protein self‐assembly has attracted great interest over the decades, due to the important role that proteins play in life. In contrast to the major achievements that have been made in the fields of DNA origami, RNA, and synthetic peptides, methods for the design of self‐assembling proteins have progressed more slowly. This Concept article provides a brief overview of studies on native protein and artificial scaffold assemblies and highlights advances in designing self‐assembling proteins. The discussions are focused on design strategies for self‐assembling proteins, including protein fusion, chemical conjugation, supramolecular, and computational‐aided de novo design.     

A Chiral Recognition System Orchestrated by Self‐Assembly: Molecular Chirality,Self‐Assembly Morphology,and Fluorescence Response

The newly developed oligophenylenevinylene (OPV)‐based fluorescent (FL) chiral chemosensor (OPV‐Me) for the representative enantiomeric guest, 1,2‐cyclohexanedicarboxylic acid (1,2‐CHDA: RR ‐ and SS ‐form) showed the high chiral discrimination ability, resulting in the different aggregation modes of OPV‐Me self‐assembly: RR ‐CHDA directed the fibrous supramolecular aggregate, whereas SS ‐CHDA directed the finite aggregate. The consequent FL intensity toward RR ‐CHDA was up to 30 times larger than that toward SS ‐CHDA. Accordingly, highly enantioselective recognition was achieved. Application to the chirality sensing was also possible: OPV‐Me exhibited a linear relationship between the FL intensity and the enantiomeric excess through the morphological development of stereocomplex aggregates. These results clearly show that the chiral recognition ability is manifested by the amplification cascade of the chirality difference through self‐assembly.     

Self‐Assembly of Ureido‐Pyrimidinone Dimers into One‐Dimensional Stacks by Lateral Hydrogen Bonding

Ureido‐pyrimidinone (UPy) dimers substituted with an additional urea functionality self‐assemble into one‐dimensional stacks in various solvents through lateral non‐covalent interactions. ¹H NMR and DOSY studies in CDCl₃ suggest the formation of short stacks (<10), whereas temperature‐dependent circular dichroism (CD) studies on chiral UPy dimers in heptane show the formation of much larger helical stacks. Analysis of the concentration‐dependent evolution of chemical shift in CDCl₃ and the temperature‐dependent CD effect in heptane suggest that this self‐assembly process follows an isodesmic pathway in both solvents. The length of the aggregates is influenced by substituents attached to the urea functionality. In sharp contrast, UPy dimers carrying an additional urethane group do not self‐assemble into ordered stacks, as is evident from the absence of a CD effect in heptane and the concentration‐independent chemical shift of the alkylidene proton of the pyrimidinone ring in CDCl₃.     

Hierarchical Self‐Assembly of Poly‐Pseudorotaxanes into Artificial Microtubules

Hierarchical self‐assembly of building blocks over multiple length scales is ubiquitous in living organisms. Microtubules are one of the principal cellular components formed by hierarchical self‐assembly of nanometer‐sized tubulin heterodimers into protofilaments, which then associate to form micron‐length‐scale, multi‐stranded tubes. This peculiar biological process is now mimicked with a fully synthetic molecule, which forms a 1:1 host‐guest complex with cucurbit[7]uril as a globular building block, and then polymerizes into linear poly‐pseudorotaxanes that associate laterally with each other in a self‐shape‐complementary manner to form a tubular structure with a length over tens of micrometers. Molecular dynamic simulations suggest that the tubular assembly consists of eight poly‐pseudorotaxanes that wind together to form a 4.5 nm wide multi‐stranded tubule.     

Gold Doping of Silver Nanoclusters: A 26‐Fold Enhancement in the Luminescence Quantum Yield

A high quantum yield (QY) of photoluminescence (PL) in nanomaterials is necessary for a wide range of applications. Unfortunately, the weak PL and moderate stability of atomically precise silver nanoclusters (NCs) suppress their utility. Herein, we accomplished a ≥26‐fold PL QY enhancement of the Ag₂₉(BDT)₁₂(TPP)₄ cluster (BDT: 1,3‐benzenedithiol; TPP: triphenylphosphine) by doping with a discrete number of Au atoms, producing Ag_29?xAu_x(BDT)₁₂(TPP)₄, x=1–5. The Au‐doped clusters exhibit an enhanced stability and an intense red emission around 660 nm. Single‐crystal XRD, mass spectrometry, optical, and NMR spectroscopy shed light on the PL enhancement mechanism and the probable locations of the Au dopants within the cluster.     

Rational Construction of 2D and 3D Borromean Arrayed Organic Crystals by Hydrogen‐Bond‐Directed Self‐Assembly

Borromean organic networks: The rigid and trigonal pyramidal molecule, 1,3,5‐tris(4‐carboxyphenyl)adamantane (TCA), self‐assembles into a 2D Borromean linked network by hydrogen bonds. Different linkers (methanol, phenazine, 4,4′‐bipyridine, and 4,4′‐azopyridine) result in more complex Borromean networks or a 3D polycatenation network.

     

Self‐Assembly of Azobenzene Derivatives into Organogels and Photoresponsive Liquid Crystals

A new class of coil–rod–coil molecules with an azobenzene core was synthesized. They were found to form robust organogels in several organic solvents. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), FTIR spectroscopy, UV/Vis absorption spectroscopy, ¹H NMR spectroscopy, and X‐ray diffraction (XRD) revealed that in these organogels, the molecules self‐assembled into a nanofiber network with an H‐type aggregation mode under the joint effect of π–π stacking, intermolecular hydrogen bonding, and van der Waals forces. Interestingly, the incorporation of the azobenzene mesogene into the rigid core led to photoisomerizable liquid crystal materials, which exhibited quick responsiveness to light and temperature, along with the trans–cis transition stimulated by UV light and heating.