Dynamic Supramolecular System Research Articles

Effects of Nucleophilic Catalysts on the Self‐Assembly of Hydrazone‐Based Supramolecular Hydrogels

AbstractCatalytic control over molecular self‐assembly provides a powerful approach to regulate the structures as well as the functionalities of supramolecular materials. Revealing how the catalysts affect the molecular self‐assembly process is crucial for rational design and control of the supramolecular self‐assembly systems. Herein, relying on a hydrazone‐based dynamic supramolecular hydrogel system, the effects of various nucleophilic catalysts on the self‐assembly of the hydrogels are investigated, demonstrating that the catalyst influences the hydrogelators self‐assembly via facilitating both the reaction and hydrogelators nucleation processes. The catalyst with higher catalytic activity accelerates the formation thereon the self‐assembly of hydrazone‐based hydrogelators, leading to hydrogels with more branched networks and higher stiffness. Importantly, we also verify that the catalysts, depending on the molecular structure, can also accelerate the self‐assembly process by affecting the hydrogelators nucleation process. These findings not only add more details to the effects of nucleophilic catalysts on the hydrazone‐based hydrogelation system, but also suggest that both the catalysis activity and chemical structures should be considered for catalytically controlled molecular self‐assembly.

Studying Cation Exchange in {Cr7Co} Pseudorotaxanes: Preparatory Studies for Making Hybrid Molecular Machines.

In the design of dynamic supramolecular systems used in molecular machines, it is important to understand the binding preferences between the macrocycle and stations along the thread. Here, we apply 1H NMR spectroscopy to investigate the relative stabilities of a series of linear alkylammonium templated pseudorotaxanes with the general formula [H2NRR'][Cr7CoF8(O2CCH2 tBu)16] by exchanging the cation in solution. Our results show that the pseudorotaxanes are able to exchange threads via a dissociative mechanism. The position of equilibrium is dependent upon the ammonium cation and solvent used. Short chain primary ammonium cations are shown to be far less favourable macrocycle stations than secondary ammonium cations. Collision-induced dissociation mass spectrometry (CID-MS) has been used to look at disassembly of the pseudorotaxanes in a solvent-free environment and stability trends compared to those in acetone-d6. The energy needed to induce 50 % of the precursor ion loss (E50) is used and shows a similar trend to the equilibria measured by NMR. The relative stabilities of these hybrid inorganic-organic pseudo-rotaxanes are different to those of host-guest compounds involving crown ethers and this may be valuable for the design of molecular machines.

Transient Metallo‐Lipidoid Assemblies Amplify Covalent Catalysis of Aqueous and Non‐Aqueous Reactions

AbstractDissipative supramolecular assemblies are hallmarks of living systems, contributing to their complex, dynamic structures and emerging functions. Living cells can spatiotemporally control diverse biochemical reactions in membrane compartments and condensates, regulating metabolite levels, signal transduction or remodeling of the cytoskeleton. Herein, we constructed membranous compartments using self‐assembly of lipid‐like amphiphiles (lipidoid) in aqueous medium. The new double‐tailed lipidoid features Cu(II) coordinated with a tetravalent chelator that dictates the binding of two amphiphilic ligands in cis‐orientation. Hydrophobic interactions between the lipidoids coupled with intermolecular hydrogen bonding led to a well‐defined bilayer vesicle structure. Oil‐soluble SNAr reaction is efficiently upregulated in the hydrophobic cavity, acting as a catalytic crucible. The modular system allows easy incorporation of exposed primary amine groups, which augments the catalysis of retro aldol and C−N bond formation reactions. Moreover, a higher‐affinity chelator enables consumption of the Cu(II) template leveraging the differential thermodynamic stability, which allows a controllable lifetime of the vesicular assemblies. Concomitant temporal upregulation of the catalytic reactions could be tuned by the metal ion concentration. This work offers new possibilities for metal ion‐mediated dynamic supramolecular systems, opening up a massive repertoire of functionally active dynamic “life‐like” materials.

Transient Metallo-Lipidoid Assemblies Amplify Covalent Catalysis of Aqueous and Non-Aqueous Reactions.

Dissipative supramolecular assemblies are hallmarks of living systems, contributing to their complex, dynamic structures and emerging functions. Living cells can spatiotemporally control diverse biochemical reactions in membrane compartments and condensates, regulating metabolite levels, signal transduction or remodeling of the cytoskeleton. Herein, we constructed membranous compartments using self-assembly of lipid-like amphiphiles (lipidoid) in aqueous medium. The new double-tailed lipidoid features Cu(II) coordinated with a tetravalent chelator that dictates the binding of two amphiphilic ligands in cis-orientation. Hydrophobic interactions between the lipidoids coupled with intermolecular hydrogen bonding led to a well-defined bilayer vesicle structure. Oil-soluble SNAr reaction is efficiently upregulated in the hydrophobic cavity, acting as a catalytic crucible. The modular system allows easy incorporation of exposed primary amine groups, which augments the catalysis of retro aldol and C-N bond formation reactions. Moreover, a higher-affinity chelator enables consumption of the Cu(II) template leveraging the differential thermodynamic stability, which allows a controllable lifetime of the vesicular assemblies. Concomitant temporal upregulation of the catalytic reactions could be tuned by the metal ion concentration. This work offers new possibilities for metal ion-mediated dynamic supramolecular systems, opening up a massive repertoire of functionally active dynamic "life-like" materials.

Lipopeptides as tools in catalysis, supramolecular, materials and medicinal chemistry.

Lipopeptides are amphiphilic peptides in which an aliphatic chain is attached to either the C or N terminus of peptides. Their self-assembly - into micelles, vesicles, nanotubes, fibres or nanobelts - leads to applications in nanotechnology, catalysis or medicinal chemistry. Self-organization of lipopeptides is dependent on both the length of the lipid tail and the amino acid sequence, in which the chirality of the peptide sequence can be transmitted into the supramolecular species. This Review describes the use of lipopeptides to design synthetic advanced dynamic supramolecular systems, nanostructured materials or self-responsive delivery systems in the area of medical biotechnology. We examine the influence of external stimuli, the ability of lipopeptide-derived structures to adapt over time and their application as medicinal agents with antibacterial, antifungal, antiviral or anticancer activities. Finally, we discuss the catalytic efficiency of lipopeptides, with the aim of building minimal synthetic enzymes, and recent efforts to incorporate metals into lipopeptide assemblies.

Visible-light controlled supramolecular transformations of donor-acceptor Stenhouse adducts amphiphiles at multiple length-scale

Designing responsive, adaptive, and dynamic supramolecular systems in water, the incorporation of photoresponsive units in amphiphilic molecular structures enables functional responses in a non-invasive way by using light. However, in aqueous media, vast majority of reported synthetic photoresponsive molecular amphiphiles are commonly driven by high energy and bio-damaging UV-light for supramolecular transformation at multiple length-scale. Herein, we present newly designed visible-light controlled supramolecular assembly of donor-acceptor Stenhouse adducts amphiphiles (DA) with excellent stability and solubility in aqueous media. The excellent photoswitchability in organic media and photoresponsiveness in aqueous media driven by visible-light are found, as confirmed with UV–vis absorption and NMR spectroscopies. Supramolecular assembly at multiple length-scale of DAs is investigated with electron microscopies and X-ray diffraction to show large aspect-ratio of nanostructures assembled into macroscopic soft scaffolds. Upon visible-light irradiation, the large geometrical transformation of DAs enables supramolecular transformations, and subsequently destabilizes the macroscopic soft scaffold to release fluorophores from the scaffolds. These results provide the feasibility in developing the next generation of visible-light controlled macroscopic soft functional scaffold from supramolecular assembly across multiple length-scale without and offer ample opportunity to design future soft robotic materials and functional biomaterials.

Dynamic Control of a Multistate Chiral Supramolecular Polymer in Water.

Natural systems transfer chiral information across multiple length scales through dynamic supramolecular interaction to accomplish various functions. Inspired by nature, many exquisite artificial supramolecular systems have been developed, in which controlling the supramolecular chirality holds the key to completing specific tasks. However, to achieve precise and non-invasive control and modulation of chirality in these systems remains challenging. As a non-invasive stimulus, light can be used to remotely control the chirality with high spatiotemporal precision. In contrast to common molecular switches, a synthetic molecular motor can act as a multistate chiroptical switch with unidirectional rotation, offering major potential to regulate more complex functions. Here, we present a light-driven molecular motor-based supramolecular polymer, in which the intrinsic chirality is transferred to the nanofibers, and the rotation of molecular motors governs the chirality and morphology of the supramolecular polymer. The resulting supramolecular polymer also exhibits light-controlled multistate aggregation-induced emission. These findings present a photochemically tunable multistate dynamic supramolecular system in water and pave the way for developing molecular motor-driven chiroptical materials.

Porphyrin-based supramolecular nanofibres as a dynamic and activatable photosensitiser for photodynamic therapy.

Photodynamic therapy (PDT) represents a promising treatment modality for a range of cancers and other non-malignant diseases due to its non-invasive nature arising from the light-dependent activation. However, PDT has not been the first-line treatment of cancer thus far as a consequence of, among others, the lack of effective transport and activation strategies, and the undesired side effect caused by skin photosensitisation induced by the "always on" photosensitisers. To overcome this "Achilles' heel", we present herein a non-covalent approach to construct a one-component dynamic supramolecular nanophotosensitising system based on a carefully designed porphyrin. The control of the photoactivities of the resulting supramolecular fibres lies in the spatiotemporal control of the monomer-polymer equilibrium. Both the thermodynamics and kinetics of this nanosystem have been carefully studied by different techniques. Moreover, in vitro and in vivo studies have also been performed, showing that these supramolecular aggregates exhibit facile cell internalisation and progressive disassembly after being endocyted by targeted cells, leading to activation of the photosensitising units and eventually cell death and tumour eradication under photoirradiation.

Solvent-Controlled Self-Assembled Oligopyrrolic Receptor.

We report a fully organic pyridine-tetrapyrrolic U-shaped acyclic receptor 10, which prefers a supramolecular pseudo-macrocyclic dimeric structure (10)2 in a less polar, non-coordinating solvent (e.g., CHCl3). Conversely, when it is crystalized from a polar, coordinating solvent (e.g., N,N-dimethylformamide, DMF), it exhibited an infinite supramolecular one-dimensional (1D) “zig-zag” polymeric chain, as inferred from the single-crystal X-ray structures. This supramolecular system acts as a potential receptor for strong acids, e.g., p-toluenesulfonic acid (PTSA), methane sulfonic acid (MSA), H2SO4, HNO3, and HCl, with a prominent colorimetric response from pale yellow to deep red. The receptor can easily be recovered from the organic solution of the host–guest complex by simple aqueous washing. It was observed that relatively stronger acids with pKa < −1.92 in water were able to interact with the receptor, as inferred from 1H NMR titration in tetrahydrofuran-d8 (THF-d8) and ultraviolet–visible (UV–vis) spectroscopic titrations in anhydrous THF at 298 K. Therefore, this new dynamic supramolecular receptor system may have potentiality in materials science research.

Light‐Fuelled Self‐Assembly of Cyclic Peptides into Supramolecular Tubules

AbstractThe work performed by supramolecular polymers, such as microtubules and actin filaments, supports the life of the cell, and essentially involves fuel‐driven self‐assembly pathways. Developing fuel‐driven supramolecular polymerization processes is therefore crucial to the realization of mechanically active molecular systems. Here, we demonstrate supramolecular tubules with non‐equilibrium steady states that are fuelled by light. This dynamic supramolecular system features rapid cycles of self‐assembly and disassembly, at rates that appear fast enough to perform mechanical tasks in fluids effectively.

Modifying the surface of peptide nanofibers utilizing a thiol‐thioester exchange

AbstractHerein, we report on the incorporation of a dithioester modification to a self‐assembling peptide and characterize a thiol‐thioester exchange on the nanofiber's surface with respect to amount of soluble exogenous thiol present and pH of the reaction. The ratios of all peptide species throughout the exchange reaction were reproducibly monitored by matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) mass spectrometry, highlighting the utility of MALDI to characterize heterogeneous and dynamic supramolecular systems. The tuneable revealing of thiols through a dynamic covalent chemical reaction presents a new strategy for labeling supramolecular surfaces. This strategy of combining reversible peptide self‐assembly and dynamic covalent chemistry opens another route for the post‐assembly modification of amyloid‐based supramolecular structures and the design of functional biomaterials.

Radical Reactions in Cavitands Unveil the Effects of Affinity on Dynamic Supramolecular Systems.

Radical reduction of alkyl halides and aerobic oxidation of alkyl aromatics are reported using water-soluble container compounds (1 and 2). The reductions involve α,ω-dihalides (4-8 and 10) with radical initiators in cavitand hosts with varied binding affinities. Product distributions lead to general guidelines for the use of dynamic supramolecular systems with fast reactions. The binding of guest substrates in the hosts must show high affinities (Ka > 103 M-1) to ensure that the reactions take place under confinement in the containers.

Aqueous highly emissive host-guest systems by host enhanced intramolecular charge transfer

Highly emissive host-guest systems have been an emerging topic which combines dynamic supramolecular system with fluorescent dyes. In this work, we report the host-guest interactions between (E)-1-benzyl-4-(2-(pyren-1-yl)vinyl)pyridin-1-ium bromide (PVP) and cucurbit[n]uril (CB[n], n = 7, 8), which were investigated in aqueous solution by 1H NMR, UV/Vis, fluorescence spectroscopic techniques and isothermal titration calorimetry (ITC). The results indicate the simultaneous formation of 1:1 inclusion complexes between CB [7] and PVP with the binding constants as 4.97 × 106 M−1. Meanwhile a 2:2 homoternary inclusion complex CB [8]-PVP with a binding constant of 2.49 × 105 M−1 was detected. The two macrocycles are found to effectively increases the fluorescence efficiency via the host-enhanced intramolecular charge transfer (ICT) effect. This system provides a distinct strategy to construct high-quantum-yield fluorescent systems.

Supramolecular Block Copolymers under Thermodynamic Control.

Supramolecular block copolymers are becoming attractive materials in nascent optoelectronic and catalytic technologies. However, their dynamic nature precludes the straightforward tuning and analysis of the polymer’s structure. Here we report the elucidation on the microstructure of triarylamine triamide-based supramolecular block copolymers through a comprehensive battery of spectroscopic, theoretical, and super-resolution microscopic techniques. Via spectroscopic analysis we demonstrate that the direct mixing of preassembled homopolymers and the copolymerization induced by slow cooling of monomers lead to the formation of the same copolymer’s architecture. The small but pronounced deviation of the experimental spectra from the linear combination of the homopolymers’ spectra hints at the formation of block copolymers. A mass balance model is introduced to further unravel the microstructure of the copolymers formed, and it confirms that stable multiblock supramolecular copolymers can be accessed from different routes. The multiblock structure of the supramolecular copolymers originates from the fine balance between favorable hydrogen-bonding interactions and a small mismatch penalty between two different monomers. Finally, we visualized the formation of the supramolecular block copolymers by adapting a recently developed super-resolution microscopy technique, interface point accumulation for imaging in nanoscale topography (iPAINT), for visualizing the architectures formed in organic media. Combining multiple techniques was crucial to unveil the microstructure of these complex dynamic supramolecular systems.

Elucidating Anion‐Dependent Formation and Conversion of Pd2L4 and Pd3L6 Metal–Organic Cages by Complementary Techniques

The fast development of the design, construction, and application of metal–organic materials including infinite metal–organic frameworks (MOFs) and discrete metal–organic cages (MOCs) has not only propelled the advance of modern supramolecular syntheses to an unprecedented level, but also burgeoned various kinds of detection and characterization technologies. Herein, complementary techniques, including diversified NMR and ESI‐MS spectrometry, solid‐state crystallography, and theoretical simulation are exploited to elucidate the structural evolution of a dynamic supramolecular coordination system involving PdII–MOCs of different compositions. The combination of various kinds of modern techniques verifies the anion template effect, which leads to the preferred formation and further conversion of Pd2L4 or Pd3L6 cages.

Photoinduced electron transfer in supramolecular ruthenium-porphyrin assemblies.

We present dynamic supramolecular systems composed of a Ru(ii) complex of the form of [Ru(dtBubpy)2(qpy)][PF6]2 (where dtBubpy is 4,4'-di-tert-butyl-2,2'-dipyridyl and qpy is 4,4':2',2'':4'',4'''-quaterpyridine) and zinc tetraphenylporphyrins (ZnTPP), through non-covalent interactions between the distal pyridine moieties of the qpy ligand and the zinc of ZnTPP. The optoelectronic properties of the assemblies and the electronic interactions between the chromophoric units have been comprehensively characterized by computational investigations, and steady-state and time-resolved emission spectroscopy. Upon photoexcitation of ZnTPP, electron transfer to the ruthenium center is thermodynamically favorable and, as a result, strong emission quenching of both units occurs.

Fluorescence quenching in β-cyclodextrin vesicles: membrane confinement and host-guest interactions.

Fluorescent β-cyclodextrin vesicles (β-CDV) that display host cavities available for host-guest interactions at the vesicle surface were prepared by incorporation of the hydrophobic spirobifluorene-based dye 1 into the membrane of unilamellar vesicles. Fluorescence quenching of dye 1 was observed in the presence of different quenchers. Methyl viologen 2 does not quench dye 1 because it does not bind to β-CDV. 4-Nitrophenol 3 and 4-nitrophenol covalently connected to adamantane 4 quench the fluorescence of dye 1 in neutral solution, but by different mechanisms according to lifetime measurements. The quenching efficiency of 3 is pH dependent due to the presence of the phenolate form. Competition experiments with excess host and guest showed that 3 is likely to diffuse in and out of the membrane, while 4 forms an inclusion complex with β-CDV leading to close contact and efficient quenching. Our findings confirm that this dynamic supramolecular system is a versatile model to investigate quenching and recognition processes in bilayer membranes.

Exploring the self-assembly and energy transfer of dynamic supramolecular iridium-porphyrin systems.

We present the first examples of dynamic supramolecular systems composed of cyclometalated Ir(iii) complexes of the form of [Ir(C^N)2(N^N)]PF6 (where C^N is mesppy = 2-phenyl-4-mesitylpyridinato and dFmesppy = 2-(4,6-difluorophenyl)-4-mesitylpyridinato and N^N is 4,4':2',2'':4'',4'''-quaterpyridine, qpy) and zinc tetraphenylporphyrin (ZnTPP), assembled through non-covalent interactions between the distal pyridine moieties of the qpy ligand located on the iridium complex and the zinc of the ZnTPP. The assemblies have been comprehensively characterized by a series of analytical techniques (1H NMR titration experiments, 2D COSY and HETCOR NMR spectra and low temperature 1H NMR spectroscopy) and the crystal structures have been elucidated by X-ray diffraction. The optoelectronic properties of the assemblies and the electronic interaction between the iridium and porphyrin chromophoric units have been explored with detailed photophysical measurements, supported by time-dependent density functional theory (TD-DFT) calculations.

ChemInform Abstract: High‐Generation Organometallic Rotaxane Dendrimer

AbstractReview: 2 refs.

Kinetic selection of polymeric guanosine architectures from dynamic supramolecular libraries

We report the constitutional resolution and selection of the dynamic supramolecular guanosine systems by using a kinetically irreversible polymerization process. We report an original strategy to transcribe and to fix supramolecular guanosine architectures in self-organized polymers. In the first resolution step, the G-quartet and G-quadruplex architectures are pre-amplified in solution in the presence of K + cations from a dynamic pool of ribbon-type or cyclic supramolecular architectures. Then in a second selection polymerization step, the G-quadruplex is kinetically fixed in a covalent polymethacrylate network via an irreversible amplification step. Both supramolecular and polymeric components mutually (synergistically) adapt their spatial constitution during simultaneous (collective) formation of micrometric self-organized hybrid domains. This contributes to the high level of adaptability and correlativity of the self-organization of the supramolecular G-quadruplexes and of the polymeric systems. Biomimetic-type hybrid systems can be generated by using this strategy.