Self-assembled peptide nanostructures: the design of molecular building blocks and their technological utilization

In this tutorial review the process and applications of peptide self-assembly into nanotubes, nanospheres, nanofibrils, nanotapes, and other ordered structures at the nano-scale are discussed. The formation of well-ordered nanostructures by a process of self-association represents the essence of modern nanotechnology. Such self-assembled structures can be formed by a variety of building blocks, both organic and inorganic. Of the organic building blocks, peptides are among the most useful ones. Peptides possess the biocompatibility and chemical diversity that are found in proteins, yet they are much more stable and robust and can be readily synthesized on a large scale. Short peptides can spontaneously associate to form nanotubes, nanospheres, nanofibrils, nanotapes, and other ordered structures at the nano-scale. Peptides can also form macroscopic assemblies such as hydrogels with nano-scale order. The application of peptide building blocks in biosensors, tissue engineering, and the development of antibacterial agents has already been demonstrated.     

Self-assembly of anisotropic tethered nanoparticle shape amphiphiles

The varied and exotic shapes of new nanoscale organic and inorganic building blocks provide new opportunities to engineer materials possessing specific functionality and physical properties dictated by the unique packings of these particles. We briefly review some of the current strategies for inducing the self-assembly of these building blocks focusing on one strategy in particular—the attachment of tethers to the building blocks at precise locations to create tethered nanoparticle “shape amphiphiles”. We use computer simulation to demonstrate that the resulting anisotropy imparted to nanocrystals or nanocolloids by the tethers can be used to encode simple design rules into the building blocks that ultimately result in a unique self-assembled structure. We present a general classification scheme for tethered nanoparticles wherein the anisotropy of a shape amphiphile is described by a vector comprised of one or more axes each describing a measure of anisotropy.     

The Role of Guest Molecules in the Self-assembly of Metal—ligand Clusters

Abstract

Understanding the self-assembly of nanoscale metal—ligand clusters is an important research area in supramolecular chemistry, especially, if one wishes to develop a truly predictive design strategy for synthesizing these nanoscale clusters. As the building blocks for forming these clusters have become larger and more complex, spacious clusters have been synthesized which often contain large cavities. These assemblies can house guest molecules which play a previously uncharacterized role in the self-assembly processes. We seek to analyze this role: do these guest molecules act as templates? Are the guest molecules necessary for cluster formation? Does the guest drive cluster assemble by forming a stable host—guest complex with the cluster? Must a truly rational design strategy for forming metal—ligand clusters incorporate the use of templates? The role of guest molecules in the self-assembly of nanoscale coordination clusters is reviewed in this article.     

Engineering Mechanical Strong Biomaterials Inspired by Structural Building Blocks in Nature

The intricate multiscale architectures in natural structural building blocks provide many sources of inspiration for the designs of artificial biomaterials. In nature, the assembly of highly ordered molecular crystals and amorphous aggregates often derives from inter- and intra-molecular interactions of biomacromolecules, e.g., proteinaceous materials. The structural biomaterials derived from the protein self-assembly behave with remarkable mechanical performance. However, there is still a grand challenge to mimic the mechanical properties of natural protein-based biomaterials in a rational design fashion to yield comparable man-made synthetic ensembles. In this review, a brief perspective on current challenges and advances in terms of bioinspired structural materials is presented. We outline a framework for mimicking protein self-assembly of natural building blocks across multiscale and highlight the critical role of synthetic biology and chemical modifications in material biosynthesis. Particularly, we focus on the design and promising applications of protein-based fibers, adhesives, dynamic hydrogels and engineered living materials, in which natural mechanical functions are effectively reproduced.     

Emergent Self-Assembly Pathways to Multidimensional Hierarchical Assemblies using a Hetero-Seeding Approach

The controlled formation of complex and functional 1-, 2-, and 3D hierarchical assemblies from molecular building blocks represents a key current challenge. Herein, we report the use of a seeded growth approach for a series of perylenediimide-based molecules (PDIs 1 – 4 ) to access otherwise inaccessible self-assembly pathways that yield complex hierarchical structures. The key to the new approach is to use hetero-seeds which possess a different composition and morphology from that of the molecular building block. For example, a nanotube seed (from PDI 3 ) and a microribbon seed (from PDI 4 ) were found to initiate different self-assembly pathways for PDI 1 , which normally assembles to yield nanocoils. This led to the formation of unprecedented 3D scroll-like and scarf-like hierarchical nanostructures, respectively. Also, the hetero-seeds from PDI 3 initiate hidden self-assembly pathways of PDI 2 to generate 1D tubular heterojunctions. Significantly, this new strategy offers new opportunities to create emergent and functional hierarchical and complex structures from small molecule precursors.     

Self-assembly of inorganic nanoparticle vesicles and tubules driven by tethered linear block copolymers

Controllable self-assembly of nanoscale building blocks into larger specific structures provides an effective route for the fabrication of new materials with unique optical, electronic, and magnetic properties. The ability of nanoparticles (NPs) to self-assemble like molecules is opening new research frontiers in nanoscience and nanotechnology. We present a new class of amphiphilic "colloidal molecules" (ACMs) composed of inorganic NPs tethered with amphiphilic linear block copolymers (BCPs). Driven by the conformational changes of tethered BCP chains, such ACMs can self-assemble into well-defined vesicular and tubular nanostructures comprising a monolayer shell of hexagonally packed NPs in selective solvents. The morphologies and geometries of these assemblies can be controlled by the size of NPs and molecular weight of BCPs. Our approach also allows us to control the interparticle distance, thus fine-tuning the plasmonic properties of the assemblies of metal NPs. This strategy provides a general means to design new building blocks for assembling novel functional materials and devices.     

pH tunable self-assembly of chicoric acid and their biocompatibility studies

We report for the first time, the pH tunable self-assembly of chicoric acid, an HIV-I integrase inhibitor, which displayed a remarkable tendency to self-assemble at room temperature into varying nano- and microstructures. Furthermore, those assemblies were then functionalised with gold (Au) nanoparticles. We then investigated the biocompatibility of the materials by conducting in vitro cell attachment and cytotoxicity studies using normal rat kidney cells. The studies revealed that the biomaterials were non-toxic and biocompatible, and showed considerable adhesion to the cells. These results suggest that the assemblies could potentially be used for a variety of applications, such as carriers for targeted drug delivery as well as optoelectronics and sensors. Furthermore, the formation of highly organised nano- and microstructures of medicinally significant phytohormones such as chicoric acid is of particular interest as it might help in further understanding the supramolecular assembly mechanism of higher organised biological structures for the development of building blocks for various device fabrications.     

Self-assembly of supramolecular platinum complexes with bis-4-pyridyl cavitands

The design and self-assembly of six new supramolecular complexes (four triangles and two 2+2 assemblies) are described. These assemblies incorporate two new bispyridyl cavitand building blocks and were prepared in excellent yields (85-95%). The assemblies and building blocks were characterized with multinuclear NMR spectroscopy, electrospray ionization mass spectrometry, and elemental analysis. Isotopically resolved mass spectrometry along with NMR data confirms the existence of the six assemblies.     

Programming supramolecular peptide materials by modulating the intermediate steps in the complex assembly pathway: Implications for biomedical applications

Self-assembling peptides form a prominent class of supramolecular materials with in general good biocompatibility. To afford better control over the material properties, tremendous progress has been made in studying the supramolecular organization of the peptide assemblies. This knowledge has helped us to understand the correlation between the molecular structure of the peptide building blocks and the properties of the supramolecular products. However, peptide self-assembly consists of a complex pathway rather than a spontaneous thermodynamic process. This implies that the outcome of the self-assembly is critically governed by the assembly pathway. Here, we are going to discuss how peptide self-assembly can be modulated at the intermediate steps in the self-assembly pathway. The focus will be to demonstrate this engineering approach on the example of zero-dimensional/one-dimensional nanostructure selectivity over the β-sheet assembly pathway. In addition, we provide examples of biomedical applications of such steered peptide assemblies in the field of drug delivery and tissue engineering.     

Welding of gold nanoparticles on graphitic templates for chemical sensing

Controlled self-assembly of zero-dimensional gold nanoparticles and construction of complex gold nanostructures from these building blocks could significantly extend their applications in many fields. Carbon nanotubes are one of the most promising inorganic templates for this strategy because of their unique physical, chemical, and mechanical properties, which translate into numerous potential applications. Here we report the bottom-up synthesis of gold nanowires in aqueous solution through self-assembly of gold nanoparticles on single-walled carbon nanotubes followed by thermal-heating-induced nanowelding. We investigate the mechanism of this process by exploring different graphitic templates. The experimental work is assisted by computational studies that provide additional insight into the self-assembly and nanowelding mechanism. We also demonstrate the chemical sensitivity of the nanomaterial to parts-per-billion concentrations of hydrogen sulfide with potential applications in industrial safety and personal healthcare.     

Self-assembly of “patchy” nanoparticles: a versatile approach to functional hierarchical materials

The solution-phase self-assembly or “polymerization” of discrete colloidal building blocks, such as “patchy” nanoparticles and multicompartment micelles, is attracting growing attention with respect to the creation of complex hierarchical materials. This approach represents a versatile method with which to transfer functionality at the molecular level to the nano- and microscale, and is often accompanied by the emergence of new material properties. In this perspective we highlight selected recent examples of the self-assembly of anisotropic nanoparticles which exploit directional interactions introduced through their shape or surface chemistry to afford a variety of hierarchical materials. We focus in particular on the solution self-assembly of block copolymers as a means to prepare multicompartment or “patchy” micelles. Due to their potential for synthetic modification, these constructs represent highly tuneable building blocks for the fabrication of a wide variety of functional assemblies.     

Peptide-Based Optical/Electronic Materials: Assembly and Recent Applications in Biomedicine,Sensing, and Energy Storage

The unique optical and electronic properties of living systems are impressive. Peptide-based supramolecular self-assembly systems attempt to mimic these properties by preparation optical/electronic function materials with specific structure through simple building blocks, rational molecular design, and specific kinetic stimulation. From the perspective of building blocks and assembly strategies, the unique optical and electronic properties of peptide-based nanostructures, including peptides self-assembly and peptides regulate the assembly of external function subunits, are systematically reviewed. Additionally, their applications in biomedicine, sensing, and energy storage are also highlighted. This bioinspired peptide-based function material is one of the hot candidates for the new generation of green intellect materials, with many advantages such as biocompatibility, environmental friendliness, and adjustable morphology.     

Fluorescent assemblies: Synergistic of amphiphilic molecules and fluorescent elements

In recent years, fluorescent assemblies based amphiphilic molecules have gained attention as unique and powerful materials for multiple applications that cover sensors, optoelectronics and bioimaging because of amphiphilic molecules self-assembly with outstanding flexibility and diversity spanning assembly structure from micelles, vesicles and nano-assemblies to gels. Weak and noncovalent interactions are important driving force for assemblies. The combination of the structural characteristics of self-assembly and the fluorescent properties of the fluorescent building element render the fluorescent material versatility and their easy-to-tune properties. Amphiphilic molecules can be used as building elements to co-assemble with dye molecules, aggregation-induced emission (AIE) gens, fluorescent nanoparticles and new amphiphilic molecules containing fluorescent groups can also be designed and prepared with self-assembly capability. Concomitantly, the improvement of fluorescence performance including fluorescence intensity, quantum yield, stability and controllability during assembly proved outstanding properties of fluorescence assemblies. These promising fluorescent assemblies are by far not exhaustive in construction method and mechanism explanation but foreshadow their more potential applications. Here, we will understand deeper the fluorescent assemblies and inspire future developments and applications employing this emerging fluorescence soft materials.     

Precise and Controllable Assembly of Block Copolymers†

With the development of nanotechnology, the precise synthesis of nanoparticles with nicely-defined dimensions and structures has been well-developed, and the functionalization and subsequent applications of the resultant nanostructures are becoming increasingly important. Comparing to inorganic nanoparticles, the nanostructures based on soft matters, especially block copolymer assemblies, are much lower in cost, easier to fabricate and richer in morphology. However, the dimensional control over the block copolymer assemblies is not as easy. Only in recent decade, with the discovery of living Crystallization-Driven Self-Assembly (CDSA) by Manners and Winnik, researchers become able to precisely tune the sizes of block copolymer assemblies in a relatively wide range. This discovery has inspired tremendous research effort in the self-assembly field, and considerable progress has been made recently. This review summarizes the main progress in the precise and controllable self-assembly field in the past five years, and is mostly focused on four aspects, including in-depth understanding of the assembly methods, extension of this method to two-dimensional nanostructures, utilization of this method to fabricate hierarchical structures, and the potential applications of these well-defined nanostructures. We hope not only to make a periodic systematic summary of previous studies, but also to provide some useful thinking for the future development of this field.     

Recent advances in biocompatible supramolecular assemblies for biomolecular detection and delivery

Inspired by sophisticated biological structures and their physiological processes,supramolecular chemistry has been developed for understanding and mimicking the behaviors of natural species. Through spontaneous self-assembly of functional building blocks,we are able to control the structures and regulate the functions of resulting supramolecular assemblies.Up to now,numerous functional supramolecular assemblies have been constructed and successfully employed as molecular devices, machines and biological diagnostic platforms.This review will focus on molecular structures of functional molecular building blocks and their assembled superstructures for biological detection and delivery.     

Super crystal structures of octahedral c-In2O3 nanocrystals

The three-dimensional self-assembly of a nanocrystal superlattice, i.e., a super crystal, has attracted increasing attention. The small building blocks for assemblies are usually spherical nanocrystals. Recent progress indicates that it is possible to achieve a super crystal using cubic nanocrystals. We further analyze and describe two-dimensional and some three-dimensional assemblies of uniform cubic-phase In2O3 nanocrystals with an octahedral shape. In this article, we demonstrate our amazing observations on these kinds of super crystals (or superlattices) as a model system, report their scale in at least tens of microns, and show other interesting features such as steps, terraces, kinks, and vacancies which are similar to those from a single crystal. Based on electron microscopy observations, three types of well-defined octahedral nanocrystal packed structures in such super crystal systems are also identified. The investigation of octahedral super crystal systems provides an alternate direction in research that may extend the interest of superlattice study to a broad spectrum by enriching and varying the shape of elemental building blocks. This may potentially result in new concepts and more challenging applications such as soft X-ray photonics.     

Self-assembled nanostructures of oligopyridine molecules

The high potential of self-assembly processes of molecular building blocks is reflected in the vast variety of different functional nanostructures reported in the literature. The constituting units must fulfill several requirements like synthetic accessibility, presence of functional groups for appropriate intermolecular interactions and depending on the type of self-assembly processsignificant chemical and thermal stability. It is shown that oligopyridines are versatile building blocks for two- and three-dimensional (2D and 3D) self-assembly. They can be employed for building up different architectures like gridlike metal complexes in solution. By the appropriate tailoring of the heterocycles, further metal coordinating and/or hydrogen bonding capabilities to the heteroaromatic molecules can be added. Thus, the above-mentioned architectures can be extended in one-step processes to larger entities, or in a hierarchical fashion to infinite assemblies in the solid state, respectively. Besides the organizational properties of small molecules in solution, 2D assemblies on surfaces offer certain advantages over 3D arrays. By precise tailoring of the molecular structures, the intermolecular interactions can be fine-tuned expressed by a large variety of resulting 2D patterns. Oligopyridines prove to be ideal candidates for 2D assemblies on graphite and metal sufaces, respectively, expressing highly ordered structures. A slight structural variation in the periphery of the molecules leads to strongly changed 2D packing motifs based on weak hydrogen bonding interactions. Such 2D assemblies can be exploited for building up host-guest networks which are attractive candidates for manipulation experiments on the single-molecule level. Thus, "erasing" and "writing" processes by the scanning tunneling microscopy (STM) tip at the liquid/solid interface are shown. The 2D networks are also employed for performing coordination chemistry experiments at surfaces.     

Self-Assembly of Polyoxometalate-Based Sub-1 nm Polyhedral Building Blocks into Rhombic Dodecahedral Superstructures

Self-assembly of subnanometer (sub-1 nm) scale polyhedral building blocks can yield some superstructures with novel and interesting morphology as well as potential functionalities. However, achieving the self-assembly of sub-1 nm polyhedral building blocks is still a great challenge. Herein, through encapsulating the titanium-substituted polyoxometalate (POM, K₇PTi₂W₁₀O₄₀) with tetrabutylammonium cations (TBA⁺), we first synthesized a sub-1 nm rhombic dodecahedral building block by further tailoring the spatial distribution of TBA⁺ on the POM. Molecular dynamics (MD) simulations demonstrated the eight TBA⁺ cations interacted with the POM cluster and formed the sub-1 nm rhombic dodecahedron. As a result of anisotropy, the sub-1 nm building blocks have self-assembled into rhombic dodecahedral POM (RD-POM) assemblies at the microscale. Benefiting from the regular structure, Br⁻ ions, and abundant active sites, the obtained RD-POM assemblies exhibit excellent catalytic performance in the cycloaddition of CO₂ with epoxides without co-catalysts. This work provides a promising approach to tailor the symmetry and structure of sub-1 nm building blocks by tuning the spatial distribution of ligands, which may shed light on the fabrication of superstructures with novel properties by self-assembly.     

Pyrrolic Amide: A New Hydrogen Bond Building Block for Self-assembly

Molecular self-assembly has emerged as a powerful technology for the synthesis of nanostructured materials. In design of various molecular assemblies, hydrogen bonding is a preferably selected intra- or inter-molecular weak interaction in recent research by virtue of the directionality and specificity. The research for novel hydrogen bond building blocks that self-assembly into well defined structures is great important not only for gaining an understanding of the concepts of self-assembly but also for the design of new molecular materials. Pyrrolic amide moiety has one hydrogen bond acceptor (C =O) and two hydrogen bond donors (pyrrole NH and amide NH). By deliberately design, pyrrolic amide compounds would be new kinds hydrogen bond building blocks. So, pyrrolic amide compounds 1 ～ 6, which bear one, two or three pyrrolic amide moieties respectively, were designed and synthesized.     

Precise Assembly of Polyoxometalates at Single-cluster Levels

Polyoxometalate (POM) clusters with atomic precision structures are promising candidates construct functional nanomaterials via self-assembly. Non-covalent interactions at molecular levels can govern the self-assembly of POM clusters, for which the precise control of POM-based assemblies can be realized at single-cluster levels. This mini-review focuses on the synthesis and properties of POM-based nanostructures, including amphiphilic POM assemblies and co-assemblies of POM clusters and other subnanometer building blocks. Several synthetic strategies have been developed for rational control of POM-based assemblies in terms of morphologies, compositions and properties. 1D subnanometer POM assemblies demonstrate remarkable enhanced mechanical properties due to the topological interactions between nanowires and surroundings. The in-depth understanding of POM-based assemblies may help in the design of functional nanomaterials in fundamental perspectives and applications.