Supramolecular Peptide Amphiphile Vesicles through Host-Guest Complexation

Thermodynamic Reversal and Structural Correlation of 24-Crown-8/Protonated Tryptophan and 24-Crown 8/Protonated Serine Noncovalent Complexes in the Gas Phase vs in Solution: Quantum Chemical Analysis

We investigate the structures of 24-crown-8/H+/l-tryptophan (CR/TrpH+) and 24-crown-8/H+/l-serine (CR/SerH+) noncovalent host-guest complex both in the gas phase and in an aqueous solution by quantum chemical methods. The Gibbs free energies of the complex in the two phases are calculated to determine the thermodynamically most favorable conformer in each phase. Our predictions indicate that both the carboxyl and the ammonium in CR/TrpH+ and the ammonium in the CR/SerH+ complexes in the lowest Gibbs free energy configurations form hydrogen bonds (H-bonds) with the CR host in the gas phase, while the conformer with the "naked" (devoid of H-bond with the CR host) -CO2H (and/or -OH) is much less favorable (Gibbs free energy higher by >3.6 kcal/mol). In the solution phase, however, a "thermodynamic reversal" occurs, making the higher Gibbs free energy gas-phase CR/TrpH+ and CR/SerH+ conformers thermodynamically more favorable under the influence of solvent molecules. Consequently, the global minimum Gibbs free energy structure in solution is structurally correlated with the thermodynamically much less gas-phase conformer. Discussions are provided concerning the possibility of elucidating host-guest-solvent interactions in solution from the gas-phase host-guest configurations in molecular detail.

Recent Progress of Supramolecular Chemotherapy Based on Host-Guest Interactions

Chemotherapy is widely recognized as an effective approach for treating cancer due to its ability to eliminate cancer cells using chemotherapeutic drugs. However, traditional chemotherapy suffers from various drawbacks, including limited solubility and stability of drugs, severe side effects, low bioavailability, drug resistance, and challenges in tracking treatment efficacy. These limitations greatly hinder its widespread clinical application. In contrast, supramolecular chemotherapy, which relies on host-guest interactions, presents a promising alternative by offering highly efficient and minimally toxic anticancer drug delivery. In this review, an overview of recent advancements in supramolecular chemotherapy based on host-guest interactions is provided. The significant role it plays in guiding cancer therapy is emphasized. Drawing on a wealth of cutting-edge research, herein, a timely and valuable resource for individuals interested in the field of supramolecular chemotherapy or cancer therapy, is presented. Furthermore, this review contributes to the progression of the field of supramolecular chemotherapy toward clinical application.

Evaluation of the complexation behaviour among functionalized diphenyl viologens and cucurbit[7] and [8]urils

The complexation behaviour of Diphenyl viologens (DPVs) with Cucurbit[n]urils (CB[n]) was evaluated in detail and the results were reported. In this work, we present the synthesis of various DPVs functionalised with electron withdrawing and electron donating groups (EWGs & EDGs) and investigate their complexation behaviour with CB[7] and CB [8]. Carboxylic acid functionalized DPV's (DPV-COOH) complexation with CB[8] gives additional insights, i.e., indicates hydrogen bonding plays an effective role in the complexation. The formation of a 2:2 quaternary complex of DPV-COOH/CB[8] under neutral pH conditions was supported by various analytical techniques. The complexation of DPVs with CB[7] specifies that irrespective of the functional group attached, they all form a 1:2 ternary complex, but the findings elaborate that the pattern followed in the complexation depends on the EW or EDG attached to the DPVs. The competition experiments conducted between functionalized DPVs and CB[7], CB[8] shows that they have more affinity towards CB[8] than CB[7] because of the better macrocyclic confinement effect of CB[8], as confirmed using UV-Vis spectroscopy. The binding affinity among EWG and EDG functionalised DPVs with CB[8] concludes EDG functionalised DPVs show better affinity towards CB[8], because they can form a charge transfer complex inside the CB[8] cavity. Exploring these host-guest interactions in more complex biological or environmental settings and studying their impact on the functionality of DPVs could be an exciting avenue for future research.

Revisiting organic charge-transfer cocrystals for wide-range tunable, ambient phosphorescence

Simple and efficient designs that enable a wide range of phosphorescence emission in organic materials have ignited scientific interest across diverse fields. One particularly promising approach is the cocrystallization strategy, where organic cocrystals are ingeniously formed through relatively weaker and dynamic non-covalent interactions. In our present study, we push the boundaries further by extending this cocrystal strategy to incorporate donor-acceptor components, stabilized by various halogen bonding interactions. This non-covalent complexation triggers ambient, charge-transfer phosphorescence (3CT), which can be precisely tuned across a broad spectrum by a modular selection of components with distinct electronic characteristics. At the core of our investigation lies the electron-deficient phosphor, pyromellitic diimide, which, upon complexation with different donors based on their electron-donating strength, manifests a striking array of phosphorescence emission from CT triplet states, spanning from green to yellow to reddish orange accompanied by noteworthy quantum yields. Through a systematic exploration of the electronic properties using spectroscopic studies and molecular organization through single-crystal X-ray diffraction, we decisively establish the molecular origin of the observed phosphorescence. Notably, our work presents, for the first time, an elegant demonstration of tunable 3CT phosphorescence emission in intermolecular donor-acceptor systems, highlighting their immense significance in the quest for efficient organic phosphors.

Smart organic materials based on macrocycle hosts

Innovative design of smart organic materials is of great importance for the advancement of modern technology. Macrocycle hosts, possessing cyclic skeletons, intrinsic cavities, and specific guest binding properties, have demonstrated pronounced potential for the elaborate fabrication of a variety of functional organic materials with smart stimuli-responsive characteristics. In this tutorial review, we outline the current development of smart organic materials based on macrocycle hosts as key building blocks, focusing on the design principles and functional mechanisms of the tailored systems. Three main types of macrocycle-based smart organic materials are exemplified as follows according to the distinct forms of construction patterns: (1) supramolecular polymeric materials and nanoassemblies; (2) adaptive molecular crystals; (3) smart porous organic materials. The responsive performances of macrocycle-containing smart materials in versatile aspects, including mechanically adaptive polymers, soft optoelectronic devices, data encryption, drug delivery systems, artificial transmembrane channels, crystalline-state gas adsorption/separation, and fluorescence sensing, are illustrated by discussing the representative studies as paradigms, where the roles of macrocycles in these systems are highlighted. We also provide in the conclusion part the perspectives and remaining challenges in this burgeoning field.

Molecularly Stimuli-Responsive Self-Assembled Peptide Nanoparticles for Targeted Imaging and Therapy

Self-assembly has emerged as an extensively used method for constructing biomaterials with sizes ranging from nanometers to micrometers. Peptides have been extensively investigated for self-assembly. They are widely applied owing to their desirable biocompatibility, biodegradability, and tunable architecture. The development of peptide-based nanoparticles often requires complex synthetic processes involving chemical modification and supramolecular self-assembly. Stimuli-responsive peptide nanoparticles, also termed "smart" nanoparticles, capable of conformational and chemical changes in response to stimuli, have emerged as a class of promising materials. These smart nanoparticles find a diverse range of biomedical applications, including drug delivery, diagnostics, and biosensors. Stimuli-responsive systems include external stimuli (such as light, temperature, ultrasound, and magnetic fields) and internal stimuli (such as pH, redox environment, salt concentration, and biomarkers), facilitating the generation of a library of self-assembled biomaterials for biomedical imaging and therapy. Thus, in this review, we mainly focus on peptide-based nanoparticles built by self-assembly strategy and systematically discuss their mechanisms in response to various stimuli. Furthermore, we summarize the diverse range of biomedical applications of peptide-based nanomaterials, including diagnosis and therapy, to demonstrate their potential for medical translation.

Designed peptide amphiphiles as scaffolds for tissue engineering

Peptide amphiphiles (PAs) are peptide-based molecules that contain a peptide sequence as a head group covalently conjugated to a hydrophobic segment, such as lipid tails. They can self-assemble into well-ordered supramolecular nanostructures such as micelles, vesicles, twisted ribbons and nanofibers. In addition, the diversity of natural amino acids gives the possibility to produce PAs with different sequences. These properties along with their biocompatibility, biodegradability and a high resemblance to native extracellular matrix (ECM) have resulted in PAs being considered as ideal scaffold materials for tissue engineering (TE) applications. This review introduces the 20 natural canonical amino acids as building blocks followed by highlighting the three categories of PAs: amphiphilic peptides, lipidated peptide amphiphiles and supramolecular peptide amphiphile conjugates, as well as their design rules that dictate the peptide self-assembly process. Furthermore, 3D bio-fabrication strategies of PAs hydrogels are discussed and the recent advances of PA-based scaffolds in TE with the emphasis on bone, cartilage and neural tissue regeneration both in vitro and in vivo are considered. Finally, future prospects and challenges are discussed.

Surface Self-Assembly of Dipeptides on Porous CaCO3 Particles Promoting Cell Internalization

The self-assembling behavior of peptides and derivatives is crucial in the natural process to construct various architectures and achieve specific functions. However, the surface or interfacial self-assembly, in particular, on the surface of micro- or nanoparticles is even less systematically investigated. Here, uniform porous CaCO₃ microparticles were prepared with different charged, hydrophobic and hydrophilic surfaces to assess the self-assembling behavior of dipeptides composed of various sequences. Experimental results indicate that dipeptides with a negative charge in an aqueous solution preferred to self-assemble on the hydrophobic and positively charged surface of CaCO₃ particles, which can be ascribed to the electrostatic and hydrophobic interaction between dipeptides and CaCO₃ particles. Meanwhile, the Log p (lipid-water partition coefficient) of dipeptides has a significant effect on the self-assembling behavior of dipeptides on the surface of porous CaCO₃; dipeptides with high Log p preferred to self-assemble on the surface of CaCO₃ particles, resulting in the improved cell internalization efficiency of particles with low cytotoxicity. After loading with a model drug (doxorubicin), the particles show obvious antitumor activity in animal experiments and can reduce Dox side effects effectively.

Methods to mechanically perturb and characterize GUV-based minimal cell models

Cells shield organelles and the cytosol via an active boundary predominantly made of phospholipids and membrane proteins, yet allowing communication between the intracellular and extracellular environment. Micron-sized liposome compartments commonly known as giant unilamellar vesicles (GUVs) are used to model the cell membrane and encapsulate biological materials and processes in a cell-like confinement. In the field of bottom-up synthetic biology, many have utilized GUVs as substrates to study various biological processes such as protein-lipid interactions, cytoskeletal assembly, and dynamics of protein synthesis. Like cells, it is ideal that GUVs are also mechanically durable and able to stay intact when the inner and outer environment changes. As a result, studies have demonstrated approaches to tune the mechanical properties of GUVs by modulating membrane composition and lumenal material property. In this context, there have been many different methods developed to test the mechanical properties of GUVs. In this review, we will survey various perturbation techniques employed to mechanically characterize GUVs.

Modular Platform of Carbohydrates-modified Supramolecular Polymers Based on Dendritic Peptide Scaffolds

Glycopeptide supramolecular polymers displaying multivalent carbohydrates are particularly suitable for immune-relevant biomaterials, due to the important functions of carbohydrates in mediating cell-cell communication and modulating immune responses. However, the diversity and complexity of carbohydrates limited the generation of glycopeptide supramolecular monomers. Thereby, a modular platform of presenting various carbohydrates, especially more complex oligosaccharides, is highly desirable but remains underexplored. Here, we first prepared the linear amphiphilic glycopeptides that self-assembled into spherical nanoparticles and worm-like nanoparticles. Furthermore, the dendritic glycopeptides that self-assembled into uniform nanorods were designed to generate modular supramolecular polymers with variable functionality, via redesigning the molecular backbone. With various functional oligosaccharide-modified supramolecular polymers, the in vitro studies further indicated that these polymers were not cytotoxic to macrophages, and significantly modulated the production of proinflammatory cytokines. These findings provide a promising platform to develop supramolecular glycopeptide biomaterials with potential applications in immunomodulation and immunotherapy.

Unveiling host-guest-solvent interactions in solution by identifying highly unstable host-guest configurations in thermal non-equilibrium gas phase

We propose a novel scheme of examining the host-guest-solvent interactions in solution from their gas phase structures. By adopting the permethylated β-cyclodextrin (perm β-CD)-protonated L-Lysine non-covalent complex as a prototypical system, we present the infrared multiple photon dissociation (IRMPD) spectrum of the gas phase complex produced by electrospray ionization technique. In order to elucidate the structure of perm β-CD)/LysH⁺ complex in the gas phase, we carry out quantum chemical calculations to assign the two strong peaks at 3,340 and 3,560 cm^-1 in the IRMPD spectrum, finding that the carboxyl forms loose hydrogen bonding with the perm β-CD, whereas the ammonium group of L-Lysine is away from the perm β-CD unit. By simulating the structures of perm β-CD/H⁺/L-Lysine complex in solution using the supramolecule/continuum model, we find that the extremely unstable gas phase structure corresponds to the most stable conformer in solution.

Double helical π-aggregate nanoarchitectonics for amplified circularly polarized luminescence

The canonical double helical π-stacked array of base pairs within DNA interior has inspired the interest in supramolecular double helical architectures with advanced electronic, magnetic and optical functions. Here, we report a selective-recognized and chirality-matched co-assembly strategy for the fabrication of fluorescent π-amino acids into double helical π-aggregates, which show exceptional strong circularly polarized luminescence (CPL). The single crystal structure of the optimal combination of co-assemblies shows that the double-stranded helical organization of these π-amino acids is cooperatively assisted by both CH-π and hydrogen-bond arrays with chirality match. The well-defined spatial arrangement of the π-chromophores could effectively suppress the non-radiative decay pathways and facilitate chiral exciton couplings, leading to superior CPL with a strong figure of merit (g_lum = 0.14 and QY = 0.76). Our findings might open a new door for developing DNA-inspired chiroptical materials with prominent properties by enantioselective co-assembly initiated double helical π-aggregation.

Synthesized or self-assembled helical architectures advance the development of chiral functional materials. Here the authors report a selective-recognized and chirality-matched co-assembly strategy for the fabrication of fluorescent π-amino acids into double helical π-aggregates with exceptional strong circularly polarized luminescence

Supramolecular Hydrogels: Design Strategies and Contemporary Biomedical Applications

Self-assembly of supramolecular hydrogels is driven by dynamic, non-covalent interactions between molecules. Considerable research effort has been exerted to fabricate and optimise supramolecular hydrogels that display shear-thinning, self-healing, and reversibility, in order to develop materials for biomedical applications. This review provides a detailed overview of the chemistry behind the dynamic physicochemical interactions that sustain hydrogel formation (hydrogen bonding, hydrophobic interactions, ionic interactions, metal-ligand coordination, and host-guest interactions). Novel design strategies and methodologies to create supramolecular hydrogels are highlighted, which offer promise for a wide range of applications, specifically drug delivery, wound healing, tissue engineering and 3D bioprinting. To conclude, future prospects are briefly discussed, and consideration given to the steps required to ultimately bring these biomaterials into clinical settings.

Cucurbit[n]uril Supramolecular Assemblies-Regulated Charge Transfer for Luminescence Switching of Gold Nanoclusters

Host-guest molecular assemblies are highly desirable for precisely controlling the luminescence properties of nanomaterials. Unfortunately, the design of high-quality luminescent nanoswitches is still very challenging due to the low affinity of traditional macrocyclic molecules (e.g., cyclodextrin) and inherently sophisticated electronic structures of nanoemitters. The current work represents the first to fabricate a luminescent nanoswitch using cucurbit[n]uril supramolecular assemblies-regulated luminescence of gold nanoclusters (AuNCs). It is found that, similar to a small-molecule fluorophore-based system, the luminescence of fabricated AuNC-cationic quencher nanohybrids can be reversibly manipulated by cucurbit[7]uril through altering the key parameters of the charge transfer process including the reorganization energy and electronic coupling between charge-transfer reactants. This study demonstrates the crucial role of cucurbit[n]uril host-guest assemblies in modulating the luminescence of AuNCs and their application in luminescence switching, thus offering new avenues for the fabrication and development of optical devices and smart materials.

Room temperature charge-transfer phosphorescence from organic donor–acceptor Co-crystals

Engineering the electronic excited state manifolds of organic molecules can give rise to various functional outcomes, including ambient triplet harvesting, that has received prodigious attention in the recent past. Herein, we introduce a modular, non-covalent approach to bias the entire excited state landscape of an organic molecule using tunable ‘through-space charge-transfer’ interactions with appropriate donors. Although charge-transfer (CT) donor–acceptor complexes have been extensively explored as functional and supramolecular motifs in the realm of soft organic materials, they could not imprint their potentiality in the field of luminescent materials, and it still remains as a challenge. Thus, in the present study, we investigate the modulation of the excited state emission characteristics of a simple pyromellitic diimide derivative on complexation with appropriate donor molecules of varying electronic characteristics to demonstrate the selective harvesting of emission from its locally excited (LE) and CT singlet and triplet states. Remarkably, co-crystallization of the pyromellitic diimide with heavy-atom substituted and electron-rich aromatic donors leads to an unprecedented ambient CT phosphorescence with impressive efficiency and notable lifetime. Further, gradual minimizing of the electron-donating strength of the donors from 1,4-diiodo-2,3,5,6-tetramethylbenzene (or 1,2-diiodo-3,4,5,6-tetramethylbenzene) to 1,2-diiodo-4,5-dimethylbenzene and 1-bromo-4-iodobenzene modulates the source of ambient phosphorescence emission from the ³CT excited state to ³LE excited state. Through comprehensive spectroscopic, theoretical studies, and single-crystal analyses, we elucidate the unparalleled role of intermolecular donor–acceptor interactions to toggle between the emissive excited states and stabilize the triplet excitons. We envisage that the present study will be able to provide new and innovative dimensions to the existing molecular designs employed for triplet harvesting.

A modular, non-covalent donor–acceptor strategy is proposed to bias the excited-state manifold of organic systems and to realize unprecedented charge-transfer phosphorescence.

Controlling the lifetime of cucurbit[8]uril based self-abolishing nanozymes

Nature has evolved a unique mechanism of self-regulatory feedback loops that help in maintiaing an internal cellular environment conducive to growth, healing and metabolism. In biology, enzymes display feedback controlled...

Self-Assembly System Based on Cyclodextrin for Targeted Delivery of Cannabidiol

Cannabidiol (CBD) is one specific kind of the cannabinoid in Cannabis sativa L with a wide range of pharmacological activities. However, the poor water solubility and specificity of CBD limits its application in pharmaceutical field. For solving these problems, in this work, we successfully prepared a targeted carrier by grafting biotin (BIO) onto ethylenediamine-β-Cyclodextrin (EN-CD) in a single step to generate a functionalized supramolecule, named BIO-CD. Subsequently, an amantadine-conjugated cannabinoids (AD-CBD) was prepared and self-assembled with the BIO-CD. A series of methods were used to characterize the inclusion behavior and physicochemical properties of AD-CBD and BIO-CD. The results showed that AD-CBD entered the cavity of BIO-CD and formed a 1:1 host-guest inclusion complex. MTT assay and confocal laser scanning microscopy (CLSM) revealed that the targeting effect and anticancer activity of AD-CBD/BIO-CD inclusion complex against three human cancer cell lines were higher than BIO-CD, AD-CBD and free CBD. Moreover, the inclusion complex could release drugs under weakly acidic conditions. These results demonstrated that AD-CBD/BIO-CD inclusion complex possess excellent targeted and anticancer activity, which is hopeful to be applied in clinic as a new therapeutic approach.

Computational Reverse Engineering Analysis for Scattering Experiments (CREASE) on Vesicles Assembled from Amphiphilic Macromolecular Solutions

In this paper we present the development and validation of the "Computational Reverse-Engineering Analysis for Scattering Experiments" (CREASE) method for analyzing scattering results from vesicle structures that are commonly found upon assembly of synthetic, biomimetic, or bioderived amphiphilic copolymers in solution. The two-step CREASE method takes the amphiphilic polymer chemistry and small-angle scattering intensity profile, I exp(q), as input and determines the vesicles' structural features on multiple length scales ranging from assembled vesicle wall's individual layer thicknesses to the monomer-level packing and distribution of polymer conformations. In the first step of CREASE, a genetic algorithm (GA) is used to determine the relevant vesicle dimensions from the input macromolecular solution information and I exp(q) by identifying the structure whose computed scattering profile best matches the input I exp(q). Then in the second step, the GA-determined dimensions are used for molecular reconstruction of the vesicle structure. To validate CREASE for vesicles, we test CREASE on input scattering intensity profiles generated mathematically (termed as in silico I exp(q) vs q) from a variety of vesicle sizes with known dimensions. We also test CREASE on in silico I exp(q) vs q generated from vesicles with dispersity in all relevant dimensions, resembling real experiments. After successful validation of CREASE, we compare the CREASE-determined dimensions against those obtained from the traditional approach of fitting the scattering intensity profile to relevant analytical model in SASVIEW package. We show that CREASE performs better than or as well as the core-multishell analytical model's fitting in SASVIEW in determining vesicle dimensions with dispersity. We also show that CREASE provides structural information beyond those possible from traditional scattering analysis using the core-multishell model, such as the distribution of solvophilic monomers between the vesicle wall's inner and outer layers in the vesicle wall and the chain-level packing within each vesicle layer.

Rapid Estimation of Binding Constants for Cucurbit[8]uril Ternary Complexes Using Electrochemistry

Supramolecular complexes are of fundamental interests in biomedicines and adaptive materials, and thus facile methods to determine their binding affinity show usefulness in the design of novel drugs and materials. Herein, we report a novel approach to estimate the binding constants K_G2 of cucurbit[8]uril-methyl viologen-based ternary complexes (CB8-MV²⁺-G2) using electrochemistry, achieving high precision (±0.03) and practical accuracy (±0.32) in logK_G2 and short measurement time (<10 min). In particular, we have uncovered a linear correlation (R² > 0.8) between the reduction potential of CB8-MV²⁺-G2 ternary complexes and their reported binding constants from isothermal titration calorimetry, which allow a calibration curve to be plotted based on 25 sample complexes. Mechanistic investigation using experimental and computational approaches reveals that this correlation stems from the dynamic host-guest exchange events occurring after the electron transfer step. Binding constants of unknown ternary complexes, where G2 = hydrocarbons, were estimated, illustrating potential applications for sparsely soluble second guests.

Synergistic effect of hydrophobic and hydrogen bonding interaction-driven viologen-pyranine charge-transfer aggregates: adenosine monophosphate recognition

Understanding the role of non-covalent interactions that dictate and fine-tune the direction of self-assembly of functional molecules is crucial for developing stimuli responsive materials. Herein, we systematically designed and synthesized viologen derivatives with hydrophobic dodecyl chains and alkyl carboxylic acid functionalities. The complementary electronic and electrostatic counterpart of viologens was chosen as pyranine. Viologens comprising of a hydrophobic dodecyl chain on one terminal and hydrogen bonding alkyl carboxylic acid on the other (V1 and V2) underwent aggregation to a varying extent upon interaction with pyranine. The length of the alkyl carboxylic acid had a greater impact on the nature and morphology of the aggregates. Control molecules (V3 and V4) in which 4,4'-bipyridine was symmetrically quaternized with alkyl carboxylic acids did not aggregate upon interaction with pyranine. The delicate balance existing between the hydrophobicity of the dodecyl chains and the intermolecular hydrogen bonding interaction between the alkyl carboxylic acid groups in V1 or V2 of the corresponding charge transfer (CT) complexes was instrumental in driving the aggregation. The CT aggregates of [V1-Pyr] and [V2-Pyr] exhibited excellent stability in water which disaggregated at physiological pH. We emphasize on the importance of synergy between hydrophobic and hydrogen bonding interactions in reinforcing each other to drive the supramolecular aggregation of the CT complexes. Such pH dependent CT aggregates are of importance as scaffolds in pH controlled drug release. In the present study, the CT aggregates were evaluated for adenosine nucleotide recognition in water; [V1-Pyr] and [V2-Pyr] exhibited selective response towards adenosine monophosphate via deprotonation induced dissolution of aggregates in water leading to emission enhancement.

pH/ROS Dual-Responsive Supramolecular Vesicles Fabricated by Carboxylated Pillar[6]arene-Based Host-Guest Recognition and Phenylboronic Acid Pinacol Ester Derivative

The pH and reactive oxygen species (ROS) dual-responsive supramolecular vesicle utilizing a novel host-guest molecular recognition between a phenylboronic acid pinacol ester derivative carrying long alkyl chain (PBEC₁₂A) and carboxylated pillar[6]arene (CP[6]) is developed. The host-guest complexation between CP[6] and PBEC₁₂A was first studied in aqueous solution. PBEC₁₂A was encapsulated within CP[6] forming a stable host-guest complex with a binding constant as high as 10⁶ M^-1 order of magnitude. The driving force behind such a host-guest recognition was the combination of electrostatic interaction and hydrophobic effect. Then, the self-assembly of the supra-amphiphiles of PBEC₁₂A-CP[6] host-guest complexes was investigated in aqueous solution through high-resolution transmission electron microscope and dynamic light scattering. It was found that the supra-amphiphiles self-assembled into supramolecular vesicles and the size of the self-assembled supramolecular vesicles could be tuned from 25 to 200 nm by varying the ratio of CP[6] to PBEC₁₂A. To demonstrate the pH- and ROS-responsive properties of the self-assembled vesicles, the supramolecular vesicles self-assembled from PBEC₁₂A/CP[6] (5:1) were utilized. The Nile Red loading and release studies demonstrated that the supramolecular vesicles possessed good pH/ROS dual-responsive properties. This study enriches the field of supra-amphiphile based on noncovalent interactions. It is anticipated that the pH/ROS dual-responsive supramolecular vesicles have potential applications in drug-delivery systems because both the stimuli are in close relation with specific microenvironments of tumors and relevant diseases of the human body.

Gel Formed by Self-Assembly of a Urea-Modified Monopyrrolotetrathiafulvalene Derivative Displays Multi-Stimuli Responsiveness and Absorption of Rhodamine B

A new monopyrrolotetrathiafulvalene-based derivative containing a urea group was designed, synthesized and thoroughly characterized. It proved to be a non-gelator in a single solvent even when heated or sonicated. However, it could self-assemble in a CHCl₃ (CH₂ Cl₂ )/n-hexane mixture to form a thermo-responsive supramolecular organogel. SEM, FT-IR spectroscopy, UV/Vis absorption spectroscopy, and SAXS revealed that in the organogel system, the gelators self-assembled into supramolecular networks with a J-type aggregation mode under the joint effect of π-π stacking, intermolecular hydrogen-bonding, and van der Waals forces. Interestingly, the gel phase was shown to undergo reversible gel-sol transformation induced by Fe³⁺ -Vitamin C (Vc), trifluoroacetic acid-triethylamine (TFA-TEA) and picric acid (PA)-NaOH. In particular, in the presence of picric acid, the experimental results proposed that charge transfer occurred from the electron-donor gelator to the electron-acceptor picric acid due to the possibility of complex formation. Furthermore, the formed organogel could behave as the matrix for encapsulating cationic fluorescent dye from wastewater, and the adsorption efficiency was directly proportional to the concentration of the gelator.

A Selective Cucurbit[8]uril-Peptide Beacon Ensemble for the Ratiometric Fluorescence Detection of Peptides

A convenient supramolecular strategy for constructing a ratiometric fluorescent chemosensing ensemble, consisting of a macrocyclic host (cucurbit[8]uril CB[8]), and a pyrene-tagged amphiphilic peptide beacon (AP 1), is reported. AP 1 unfolds upon encapsulation of the pyrene termini into the hydrophobic CB[8] cavity. This changes pyrene excimer to monomer emission. Substrates with higher affinity for the CB[8] cavity can displace AP 1 from the ensemble. The released AP 1 folds again to form a pyrene excimer, which allows for the ratiometric fluorescence monitoring of the substrate. In this report, the ensemble capacity for ratiometric fluorescence monitoring of biological substrates, such as amino acid derivatives, specific peptides, and proteins, in aqueous media is demonstrated.

Preparation and Properties of Semi-Self-Assembled Lipopeptide Vesicles

Novel lipopeptide vesicles are prepared from self-assembled nanomembranes through an extrusion method. The size of vesicles can be controlled by the pore diameter of the extrusion filter. The vesicles are rather stable because hydrogen bonds exist among the peptide headgroups. When doxorubicin hydrochloride (DOX·HCl) is encapsulated in the vesicles, it could be released sustainably, and its side effect would also be reduced due to encapsulation. The leakage rate of DOX·HCl depends on the pH via charge regulation. As drug carriers, lipopeptide vesicles have been proved to have nontoxicity to normal cells. A magnetic surfactant CH₃(CH₂)₁₄CH₂N(CH₃)₃⁺ [FeCl₃Br]^- (CTAFe) was mixed with lipopeptide to modify the vesicles. Also, the results demonstrated that the vesicles is endowed with magnetic property after the addition of CTAFe. We believe that the strategy of lipopeptide vesicle preparation would enrich the drug carrier family and expand the application of lipopeptide materials.

Applications of Cucurbiturils in Medicinal Chemistry and Chemical Biology

The supramolecular chemistry of cucurbit[n]urils (CBn) has been rapidly developing to encompass diverse medicinal applications, including drug formulation and delivery, controlled drug release, and sensing for bioanalytical purposes. This is made possible by their unique recognition properties and very low cytotoxicity. In this review, we summarize the host-guest complexation of biologically important molecules with CBn, and highlight their implementation in medicinal chemistry and chemical biology.

Freeze the dynamicity: charge transfer complexation assisted control over the reaction pathway

Aqueous CT complexes of donor and acceptor molecules with reactive thiol groups were frozen and lyophilized to get alternate D–A assemblies in the solid state. Oxidation of the thiols resulted in asymmetric disulfides exclusively.

Charge transfer (CT) complexes between electron donor and acceptor molecules provide unique alternate D–A arrangements. However, these arrangements cannot be fully translated into chemo-selective organic transformations as the dynamicity of CT complexes in solution results in the co-existence of D–A assemblies and free monomers during the reaction time-scale. A conceptually new strategy to exploit CT complexes toward chemo-selective products by means of seizing the dynamicity of CT complexes is reported here. Aqueous CT complexes of donor and acceptor molecules bearing reactive thiol groups were frozen instantly and cryo-desiccated to get the alternate D–A assemblies intact in the solid state. Oxidation of reactive thiols in an oxygen rich solvent in the solid state resulted in the formation of the hetero-dimer exclusively. CT complexation and appropriate molecular arrangements are the key factors behind successful execution of this novel methodology. The strategy also paves the way to prepare unsymmetrical disulfide molecules from two dissimilar thiols.

Designer Peptide Amphiphiles: Self-Assembly to Applications

Peptide amphiphiles (PAs) are extremely attractive as molecular building blocks, especially in the bottom-up fabrication of supramolecular soft materials, and have potential in many important applications across various fields of science and technology. In recent years, we have designed and synthesized a large group of peptide amphiphiles. This library of PAs has the ability to self-assemble into a variety of aggregates such as fibers, nanosphere, vesicles, nanosheet, nanocups, nanorings, hydrogels, and so on. The mechanism behind the formation of such a wide range of structures is intriguing. Each system has its individual method of aggregation and results in assemblies with important applications in areas including chemistry, biology, and materials science. The aim of this feature article is to bring together our recent achievements with designer PAs with respect to their self-assembly processes and applications. Emphasis is placed on rational design, mechanistic aspects of the self-assembly processes, and the applications of these PAs. We hope that this article will provide a conceptual demonstration of the different approaches taken toward the construction of these task-specific PAs.

Functionalized pyrene-based AIEgens: synthesis, photophysical characterization and density functional theory studies

Three new pyrene-based derivatives P1, P2 and P3 with a substituted pyrazole were designed, synthesized and characterized using standard spectroscopic techniques. Ultraviolet-visible (UV-vis) spectroscopic studies for P1-P3 uncovered a finite bathochromic shift of the molecules in solvents of varying polarity. Photoluminescence (PL) studies revealed the significant fluorescence emission of all molecules in higher polar solvents such as MeOH and dimethylformamide (DMF). Fluorescence quantum yield studies demonstrated the importance of P3 possessing cyanofunctionality for imparting higher emission with a quantum yield of 0.36%. Ratiometric studies performed in a tetrahydrofuran (THF)/H₂ O mixture indicated fluorescence enhancement with increasing overall percentage of water, confirming the aggregation-induced emission effect. Cyclic voltammetry study of molecules P1-P3 revealed an irreversible oxidation peak and the band gaps were calculated to be 2.26 eV for P1 and 2.31 eV for P2 and P3 respectively. Density functional theory (DFT) studies performed on molecules P1-P3 validate the structure correlation of the molecules. Theoretically estimated highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and bandgap correlated well with the experimental values. Furthermore, time-dependent (TD)DFT showed that the major contribution for the electronic transitions occurring in the system was governed by HOMO-1 and LUMO+1 orbitals.

Shape-Controlled Dodecaborate Supramolecular Organic-Framework-Supported Ultrafine Trimetallic PtCoNi for Catalytic Hydrolysis of Ammonia Borane

On the basis of the unique chaotropic supramolecular assembly of cucurbit[5]uril (CB5) and dodecahydro- closo-dodecaborate anion [ closo-B₁₂H₁₂]^2-, we have developed an efficient and universal platform to fabricate shape-controlled dodecaborate-based supramolecular organic frameworks (BOFs) decorated with ultrafine monodispersed trimetallic alloys. Simply by regulating the molar ratio of CB5 and [ closo-B₁₂H₁₂]^2-, a series of fascinating morphologies, such as flowerlike structures, nanorods, nanocubes, and nanosheets, were successfully constructed. These obtained BOFs were proved to be good substrate supports for in situ synthesis of trimetallic PtCoNi nanoalloys, where the final PtCoNi-BOFs materials were obtained efficiently as a precipitate from aqueous solutions, and showed excellent catalytic performance in ammonia borane hydrolysis with a high turnover frequency of 1490 mol_H2 mol_Pt^-1 min^-1 and a low activation energy of 15.79 kJ mol^-1.

Ultrasound and Redox-Triggered Morphology Transitions of Supramolecular Self-assemblies with pH Responsiveness for Triple-Controlled Release

The realization of multistage-controlled drug delivery at the cell level through the morphology transitions of supramolecular self-assemblies (SSA) is still a challenge. Herein, successive morphology transitions of SSA with pH responsiveness were successfully achieved through the subsequent action of ultrasound and redox stimuli. Specifically, we first prepared noncovalently PEGylated spherical self-assemblies formed by host-guest-conjugated amphiphilic β-CD dimers. The functionalized PEG could be associated/disassociated onto the spherical self-assemblies by adjusting pH values of solutions. They could reassemble into branched self-assemblies induced by ultrasonication. Such branched self-assemblies could be further dissociated into second spherical self-assemblies under a redox stimulus. This morphology transition process was used to conduct triple-controlled targeted drug delivery and release in cancer cells. This work will be beneficial for the design of smart SSA for controlled release in vivo.

Assembly and Evolution of Gemini-Type Peptide Amphiphile with a Di-Lysine Spacer

Peptide amphiphiles (PAs) can self-assemble into a variety of supramolecular structures with excellent biofunctions. However, their assembly with time has rarely been observed and reported. Here, we find that a novel gemini-type PA [12-(Lys)₂-12], taking two lysine (Lys) groups as the spacer, shows an obvious assembly and evolution process with time. Driven by the strong hydrophobic interaction between the alkyl chains as well as the electrostatic force and hydrogen bonding among the peptide spacers, the 12-(Lys)₂-12 molecules first self-assemble into vesicles and then transform into fibrils, ribbons, and belts with time. If replacing the -(Lys)₂- spacer with four lysine groups [-(Lys)₄-] or two glutamic acid groups [-(Glu)₂-], the PA molecules do not show the aggregate growth with time. This indicates that the lysine structure and its length are important structural factors contributing to the dynamic aggregate evolution behavior. More interestingly, this assembly and evolution behavior is highly dependent on 12-(Lys)₂-12 concentration. Only in the proper concentration region (0.5-0.7 mM), the self-assembly displays the aggregate growth with time. At lower or higher concentrations, the aggregate growth is largely delayed or inhibited. Moreover, we also find that the aggregate growth of 12-(Lys)₂-12 is related to the fibril solubilization temperature ( T_f→s). The faster aggregate growth occurs when the temperature is much lower than T_f→s. This work gains new insights into the evolution of the self-assembling structures of peptide amphiphiles.

Measuring Binding Constants of Cucurbituril-Based Host-Guest Interactions at the Single-Molecule Level with Nanopores

Cucurbiturils are one type of widely used macrocyclic host compound in supramolecular chemistry. Their peculiar properties have led to applications in a wide variety of research areas such as fluorescence spectroscopy, drug delivery, catalysis, and nanotechnology. However, the solubilities of cucurbiturils are rather poor in water and many organic solvents, which may cause accuracy problems when measuring binding constants with traditional methods. In this report, we aim to develop an approach to measure the binding constants of cucurbituril-based host-guest interactions at the single-molecule level. First, we covalently attach different guest compounds to the side-chain of DNA molecules. Then, excess cucurbiturils are incubated with DNA probes to form the host-guest complexes. Next, the modified DNA hybrids are threaded through α-hemolysin nanopore to generate highly characteristic current events. Finally, statistical analyses of the obtained events afford the binding constants of cucurbiturils with various molecules. This new approach provides a simple and straightforward method to compare binding strength of different host-guest complexes and may find applications for quantifying other macrocycle-based host-guest interactions.

Ultrahigh binding affinity of a hydrocarbon guest inside cucurbit[7]uril enhanced by strong host–guest charge matching

Electrostatic interactions as a strong driving force for neutral apolar host–guest complexation is revealed via a large-scale computational approach.

Tuning the aggregation of an amphiphilic anionic calix[5]arene by selective host–guest interactions with bola-type dications

Bola-type dications of different length drive the formation of head-to-tail or capsular supramolecular amphiphiles and, in turn, that of the final aggregates.

pH clock instructed transient supramolecular peptide amphiphile and its vesicular assembly

A pH clock directed transient supramolecular peptide amphiphile and its vesicular assembly using ternary complexation of cucurbit[8]uril is displayed.

LCST behavior controlled by size-matching selectivity from low molecular weight monomer systems

LCST behavior was controlled by crown ether–cation recognition motifs via size-matching selectivity.

Cucurbit[n]uril-based amphiphiles that self-assemble into functional nanomaterials for therapeutics

In this feature article, the two types (molecular amphiphile and supramolecular amphiphile) of CB-based amphiphiles, their self-assemblies and their applications for useful nanotherapeutics and theranostics are presented with future perspectives.

Disulfide crosslinking and helical coiling of peptide micelles facilitate the formation of a printable hydrogel

Tripeptides self-assembled into aligned micelles which transformed into nanohelices via covalent and noncovalent interactions to give a printable hydrogel.

A triply-responsive supramolecular vesicle fabricated by α-cyclodextrin based host-guest recognition and double dynamic covalent bonds

The supramolecular construction of multi-stimuli assemblies is a challenging task for prospective use. In this work, a novel supramolecular amphiphile was fabricated by introducing molecules with dynamic covalent bonds into host-guest inclusion. The amphiphile formed a vesicle, which was characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), 1H NMR and UV-vis spectra. Furthermore, the vesicular structure could be regulated by pH, light and redox reagent, and thus the loaded dye in the vesicles could be released in a controlled manner.

Programmable Multicomponent Self-Assembly Based on Aromatic Amino Acids

Construction of integrated self-assembly with ordered structures from two or more organic building blocks is currently a challenge, since it suffers from intrinsic systematic complexity and diverse competitive pathways. Here, it is reported that aromatic amino acid building units can be incorporated into two- or three-component coassembly driven primarily by hydrogen bonding interactions without the assistance of metal-ligand and macrocycle-based host-guest interactions. The key strategy is to employ a C₃ -symmetric molecule with alternative hydrogen bonding donor/acceptor sites that are able to bind either carboxylic acid or pyridine appended building units. Aromatic amino acids, C₃ -symmetric compound, and bipyridine unit constitute a unique ternary mutual binding system, where three coassembly pathways including two pairwise formations and one ternary combination are unveiled, giving rise to two- and three-component self-assemblies with ordered structures, respectively. The pathway complexity lies in the structural parameter of aromatic amino acids, which can be programmable by controlling substituents at the α-position of amino acids.