Self-Assembly of Bolaamphiphiles into 2D Nanosheets via Synergistic and Meticulous Tailoring of Multiple Noncovalent Interactions

Crystallization-Driven Controlled 2D Self-Assemblies via Aqueous RAFT Emulsion Polymerization

Aqueous emulsion polymerization is a robust technique for preparing nanoparticles of block copolymers; however, it typically yields spherical nanoassemblies. The scale preparation of nanoassemblies with nonspherical high-order morphologies is a challenge, particularly 2D core-shell nanosheets. In this study, the polymerization-induced self-assembly (PISA) and crystallization-driven self-assembly (CDSA) are combined to demonstrate the preparation of 2D nanosheets and their aggregates via aqueous reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization. First, the crucial crystallizable component for CDSA, hydroxyethyl methacrylate polycaprolactone (HPCL) macromonomer is synthesized by ring opening polymerization (ROP). Subsequently, the RAFT emulsion polymerization of HPCL is conducted to generate crystallizable nanomicelles by a grafting-through approach. This PISA process simultaneously prepared spherical latices and bottlebrush block copolymers comprising poly(N',N'-dimethylacrylamide)-block-poly(hydroxyethyl methacrylate polycaprolactone) (PDMA-b-PHPCL). The latexes are now served as seeds for inducing the formation of 2D hexagonal nanosheets, bundle-shaped and flower-like aggregation via the CDSA of PHPCL segments and unreacted HPCL during cooling. Electron microscope analysis trace the morphology evolution of these 2D nanoparticles and reveal that an appropriate crystallized component of PHPCL blocks play a pivotal role in forming a hierarchical structure. This work demonstrates significant potential for large-scale production of 2D nanoassemblies through RAFT emulsion polymerization.

Robust Multifunctional Ultrathin 2 Nanometer Organic Nanofibers

Ultrathin organic nanofibers (UTONFs) represent an emerging class of nanomaterials as they carry a set of favorable attributes, including ultrahigh specific surface area, lightweight, and mechanical flexibility, over inorganic counterparts, for use in biomedicine and nanotechnology. However, precise synthesis of uniform UTONFs (diameter ≤ 2 nm) with tailored functionalities remained challenging. Herein, we report robust multifunctional UTONFs using hydrophobic interaction-driven self-assembly of amphiphilic alternating peptoids containing hydrophobic photoresponsive azobenzene and hydrophilic hydroxyl moieties periodically arranged along the peptoid backbone. Notably, the as-crafted UTONFs are approximately 2 nm in diameter and tens of micrometers in length (an aspect ratio, AR, of ∼10000), exemplifying the UTONFs with the smallest diameter yielded via self-assembly. Intriguingly, UTONFs were disassembled into short-segmented nanofibers and controllably reassembled into UTONFs, resembling "step-growth polymerization". Photoisomerization of azobenzene moieties leads to reversible transformation between UTONFs and spherical micelles. Such meticulously engineered UTONFs demonstrate potential for catalysis, bioimaging, and antibacterial therapeutics. Our study highlights the significance of the rational design of amphiphiles containing alternating hydrophobic and hydrophilic moieties in constructing otherwise unattainable extremely thin UTONFs with ultrahigh AR and stimuli-responsive functionalities for energy and bionanotechnology.

Multiple non-covalent-interaction-directed supramolecular double helices: the orthogonality of hydrogen, halogen and chalcogen bonding

In this study, a benzoselenadiazole- and pyridine-bifunctionalized hydrogen-bonded arylamide foldamer was synthesized. A co-crystallization experiment with 1,4-diiodotetrafluorobenzene showed that a new type of supramolecular double helices, which were induced by three orthogonal interactions, namely, three-center hydrogen bonding (O⋯H⋯O), I⋯N halogen bonding and Se⋯N chalcogen bonding, have been constructed in the solid state. This work presents a novel instance of multiple non-covalent interactions that work together to construct supramolecular architectures.

Morphologically Tunable Rectangular Platelets Self-Assembled from Diblock Molecular Brushes Containing Azopyridine Pendants

Two-dimensional (2D) platelet structures are of growing importance as building blocks for the preparation of optical and electrical devices. However, the creation of morphologically tunable rectangular platelets through polymer self-assembly still remains a challenge. Herein, we describe a rational strategy for the fabrication of 2D rectangular platelets by stacking azopyridine-containing diblock molecular brushes in two dimensions in a selective solvent. Amphiphilic PEG-co-(PtBA-g-PAzoPy) DMBs with poly(ethylene glycol) (PEG) block, poly(t-butyl acrylate) (PtBA) backbone, and poly(6-(4-(4-pyridyazo)phenoxy)-hexyl methacrylate) (PAzoPy) brush were synthesized by sequential reversible addition-fragmentation chain transfer polymerization and atom transfer radical polymerization. Various rectangular platelets were obtained via the solution self-assembly of PEG-co-(PtBA-g-PAzoPy) through a heating-cooling-aging process in which the morphology and size of platelets could be controlled by adjusting the composition of DMBs as well as the solvent polarity. In addition, we investigated the metal chelation ability and H-bonding-assisted co-assembly capability of PEG-co-(PtBA-g-PAzoPy). The results displayed that 2D hybrids and flower-like platelets were formed, respectively. Our study presents an efficient method to fabricate rectangular platelets with tunable morphologies.

Hole interactions of aerogen oxides with Lewis bases: an insight into σ-hole and lone-pair-hole interactions

σ-Hole and lone-pair (lp)-hole interactions of aerogen oxides with Lewis bases (LB) were comparatively inspected in terms of quantum mechanics calculations. The ZOn ⋯ LB complexes (where Z = Kr and Xe, n = 1, 2, 3 and 4, and LB = NH3 and NCH) showed favourable negative interaction energies. The complexation features were explained in light of σ-hole and lp-hole interactions within optimum distances lower than the sum of the respective van der Waals radii. The emerging findings outlined that σ-hole interaction energies generally enhanced according to the following order: KrO4 ⋯ < KrO⋯ < KrO3⋯ < KrO2⋯LB and XeO4⋯ < XeO⋯ < XeO2⋯ < XeO3⋯LB complexes with values ranging from -2.23 to -12.84 kcal mol-1. Lp-hole interactions with values up to -5.91 kcal mol-1 were shown. Symmetry-adapted perturbation theory findings revealed the significant contributions of electrostatic forces accounting for 50-65% of the total attractive forces within most of the ZOn⋯LB complexes. The obtained observations would be useful for the understanding of hole interactions, particularly for the aerogen oxides, with application in supramolecular chemistry and crystal engineering.

Self-Assembly of Poly(Amino Acid)s Mediated by Secondary Conformations

Self-assembly of block copolymers has recently drawn great attention due to its remarkable performance and wide variety of applications in biomedicine, biomaterials, microelectronics, photoelectric materials, catalysts, etc. Poly(amino acid)s (PAAs), formed by introducing synthetic amino acids into copolymer backbones, are able to fold into different secondary conformations when compared with traditional amphiphilic copolymers. Apart from changing the chemical composition and degree of polymerization of copolymers, the self-assembly behaviors of PAAs could be controlled by their secondary conformations, which are more flexible and adjustable for fine structure tailoring. In this article, we summarize the latest findings on the variables that influence secondary conformations, in particular the regulation of order-to-order conformational changes and the approaches used to manage the self-assembly behaviors of PAAs. These strategies include controlling pH, redox reactions, coordination, light, temperature, and so on. Hopefully, we can provide valuable perspectives that will be useful for the future development and use of synthetic PAAs.

Pathway-Controlled Aqueous Supramolecular Polymerization via Solvent-Dependent Chain Conformation Effects

Solute-solvent interactions play a critical role in multiple fields, including biology, materials science, and (physical) organic, polymer, and supramolecular chemistry. Within the growing field of supramolecular polymer science, these interactions have been recognized as an important driving force for (entropically driven) intermolecular association, particularly in aqueous media. However, to date, solute-solvent effects remain poorly understood in the context of complex self-assembly energy landscapes and pathway complexity. Herein, we unravel the role of solute-solvent interactions in controlling chain conformation effects, allowing energy landscape modulation and pathway selection in aqueous supramolecular polymerization. To this end, we have designed a series of oligo(phenylene ethynylene) (OPE)-based bolaamphiphilic Pt(II) complexes OPE2-4 bearing solubilizing triethylene glycol (TEG) chains of equal length on both molecule ends, but a different size of the hydrophobic aromatic scaffold. Strikingly, detailed self-assembly studies in aqueous media disclose a different tendency of the TEG chains to fold back and enwrap the hydrophobic molecular component depending on both the size of the core and the volume fraction of the co-solvent (THF). The relatively small hydrophobic component of OPE2 can be readily shielded by the TEG chains, leading to only one aggregation pathway. In contrast, the decreased capability of the TEG chains to effectively shield larger hydrophobic cores (OPE3 and OPE4) enables different types of solvent quality-dependent conformations (extended, partly back-folded and back-folded), which in turn induce various controllable aggregation pathways with distinct morphologies and mechanisms. Our results shed light on previously underappreciated solvent-dependent chain conformation effects and their role in governing pathway complexity in aqueous media.

Self-Assembly of Functional Protein Nanosheets from Thermoresponsive Bolaamphiphiles

Nanosheets are two-dimensional materials, less than 100 nm thick, that can be used for separations, biosensing, and biocatalysis. Nanosheets can be made from inorganic and organic materials such as graphene, polymers, and proteins. Here, we report the self-assembly of nanosheets under aqueous conditions from functional proteins. The nanosheets are synthesized from two fusion proteins held together by high-affinity interactions of two leucine zippers to form bolaamphiphiles. The hydrophobic domain, Z_R-ELP-Z_R, contains the thermoresponsive elastin-like peptide (ELP) flanked by arginine-rich leucine zippers (Z_R), each of which binds the hydrophilic fusion protein, globule-Z_E, via the glutamate-rich leucine zipper (Z_E) fused to a functional, globular protein. Nanosheets form when the proteins are mixed at 4 °C in aqueous solutions and then heated to 25 °C as the container is rotated end-over-end causing expansion and contraction of the air-water interface. The nanosheets are robust with respect to the choice of globular protein and can incorporate small fluorescent proteins that are less than 30 kDa as well as large enzymes, such as 80 kDa malate synthase G. Upon incorporation into nanosheets, enzymes retain more than 70% of their original activity, demonstrating the potential of protein nanosheets to be used for biosensing or biocatalytic applications.

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.

The Assembly and Jamming of Nanoparticle Surfactants at Liquid-Liquid Interfaces

Using the interactions between nanoparticles (NPs) and polymeric ligands to generate nanoparticle surfactants (NPSs) at the liquid-liquid interface, the binding energy of the NP to the interface can be significantly increased, irreversibly binding the NPSs to the interface. By designing a simplified NPS model, where the NP size can be precisely controlled and the characteristic fluorescence of the NPs be used as a direct probe of their spatial distribution, we provide new insights into the attachment mechanism of NPSs at the liquid-liquid interface. We find that the binding energy of NPSs to the interface can be reduced by competitive ligands, resulting in the dissociation and disassembly of NPSs at the interface, and allowing the construction of responsive, reconfigurable all-liquid systems. Smaller NPSs that are loosely packed (unjammed) and irreversibly bound to the interface can be displaced by larger NPSs, giving rise to a size-dependent assembly of NPSs at the interface. However, when the smaller size NPSs are densely packed and jam at the interface, the size-dependent assembly of NPSs at the interface can be completely suppressed.

Two-Dimensional Polymers: Synthesis and Applications

Two-dimensional (2D) polymers represent an emerging class of nanomaterials possessing covalent sheet-like morphology. They display a set of intriguing properties, including large specific surface area, low density, versatile control over sizes and compositions, and high adaptability. As such, they find application in energy conversion and storage, nanotechnology, and biotechnology. However, it remains challenging to synthesize thin-layer 2D polymers with conventional methods. Herein, in this perspective, recent advances in synthesis and applications of thin-layer 2D polymers via capitalizing on various "top-down" and "bottom-up" strategies are summarized. Particularly, some new methods (e.g., free radical polymerization in solution and surfactant-monolayer-assisted interfacial synthesis) in combination with electrostatic repulsion or steric hindrance effect to engineer single-layer 2D polymers at large scale are highlighted.

Two-Dimensional Conductive π-d Frameworks with Multiple Sensory Capabilities

Two-dimensional (2D) metal-molecule hybrid frameworks have attracted great attention due to their π-d interactions for the charge-spin-lattice coupling, promising for next-generation molecular electronics. However, a high electrical conductivity is indispensable to realize such potential. Herein, we design and assemble a conductive 2D conjugated coordination thin film through an interfacial reaction between the aqueous and organic phases. Its electronic conducting properties are derived from the π-d coupling interactions to achieve an electrical conductivity of 1.05 S/cm, while the stimulus-dependent π-d interactions induce multifunctional sensory capabilities. The Co-DABDT (DABDT = 2,5-diamino-1,4-benzenedithiol dihydrochloride) thin films demonstrate an excellent performance for sensing light, strain, temperature, and humidity, as well as robust mechanical stability. The 2D frameworks with multisensing properties for real-time static and dynamic monitoring are promising for smart wearable electronic systems.