Integrating Enzymes with Supramolecular Polymers for Recyclable Photobiocatalytic Catalysis

Chemical modifications of enzymes excel in the realm of enzyme engineering due to its directness, robustness, and efficiency; however, challenges persist in devising versatile and effective strategies. In this study, we introduce a supramolecular modification methodology that amalgamates a supramolecular polymer with Candida antarctica lipase B (CalB) to create supramolecular enzymes (SupEnzyme). This approach features the straightforward preparation of a supramolecular amphiphilic polymer (β-CD@SMA), which was subsequently conjugated to the enzyme, resulting in a SupEnzyme capable of self-assembly into supramolecular nanoparticles. The resulting SupEnzyme nanoparticles can form micron-scale supramolecular aggregates through supramolecular and electrostatic interactions with guest entities, thus enhancing catalyst recycling. Remarkably, these aggregates maintain 80 % activity after seven cycles, outperforming Novozym 435. Additionally, they can effectively initiate photobiocatalytic cascade reactions using guest photocatalysts. As a consequence, our SupEnzyme methodology exhibits noteworthy adaptability in enzyme modification, presenting a versatile platform for various polymer, enzyme, and biocompatible catalyst pairings, with potential applications in the fields of chemistry and biology.

Recent Progress in Site-Selective Modification of Peptides and Proteins Using Macrocycles

Peptides and proteins undergo crucial modifications to alter their physicochemical properties to expand their applications in diverse fields. Various techniques, such as unnatural amino acid incorporation, enzyme catalysis, and chemoselective methods, have been employed for site-selective peptide and protein modification. While traditional methods remain valuable, advancement in host-guest chemistry introduces innovative and promising approaches for the selective modification of peptides and proteins. Macrocycles exhibit robust binding affinities, particularly with natural amino acids, which facilitates their use in selectively binding to specific sequences. This distinctive property endows macrocycles with the potential for modification of target peptides and proteins. This review provides a comprehensive overview of strategies utilizing macrocycles for the selective modification of peptides and proteins. These strategies unlock new possibilities for constructing antibody-drug conjugates and stabilizing volatile medications.

Noncovalent PEGylation of protein and peptide therapeutics

Clinical applications of protein therapeutics-an advanced generation of drugs characterized by high biological specificity-are rapidly expanding. However, their development is often impeded by unfavorable pharmacokinetic profiles and largely relies on the use of drug delivery systems to prolong their in vivo half-life and suppress undesirable immunogenicity. Although a commercially established PEGylation technology based on protein conjugation with poly(ethylene glycol) (PEG)-protective steric shield resolves some of the challenges, the search for alternatives continues. Noncovalent PEGylation, which mainly relies on multivalent (cooperative) interactions and high affinity (host-guest) complexes formed between protein and PEG offers a number of potential advantages. Among them are dynamic or reversible protection of the protein with minimal loss of biological activity, drastically lower manufacturing costs, "mix-and-match" formulations approaches, and expanded scope of PEGylation targets. While a great number of innovative chemical approaches have been proposed in recent years, the ability to effectively control the stability of noncovalently assembled protein-PEG complexes under physiological conditions presents a serious challenge for the commercial development of the technology. In an attempt to identify critical factors affecting pharmacological behavior of noncovalently linked complexes, this Review follows a hierarchical analysis of various experimental techniques and resulting supramolecular architectures. The importance of in vivo administration routes, degradation patterns of PEGylating agents, and a multitude of potential exchange reactions with constituents of physiological compartments are highlighted. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Monitoring Methionine Decarboxylase by Supramolecular Tandem Assay

Methionine is an essential amino acid involved in many physiological and pathological processes. Methionine starvation caused by methionine decarboxylase ( MetDC) degradation becomes a promising strategy for cancer treatment. Multistep colorimetric method, the present approach to monitor the MetDC activity, possesses drawbacks of the complicated process, low accuracy, and poor anti-interference due to indirect detecting. Herein, we report a facile and easy-to-use supramolecular tandem assay (STA) with cucurbit[7]uril and acridine orange reporter pair for the direct and real-time monitoring of MetDC activity. The applicability of this strategy for measuring enzyme-kinetic parameters and screening of inhibitors are also demonstrated. The STA for MetDC activity detection not only provides a feasible method for methionine-related disease diagnosing but also opens a perspective for cancer therapy.

Progress of albumin-polymer conjugates as efficient drug carriers

Albumin is a protein that has garnered wide attention in nanoparticle-based drug delivery of cancer therapeutics due to its natural abundance and unique cancer-targeting ability. The propensity of albumin to naturally accumulate in tumours, further augmented by the incorporation of targeting ligands, has made the field of albumin-polymer conjugate development a much pursued one. Polymerization techniques such as RAFT and ATRP have paved the path to incorporate various polymers in the design of albumin-polymer hybrids, indicating the advancement of the field since the first instance of PEGylated albumin in 1977. The synergistic combination of albumin and polymer endows manifold features to these macromolecular hybrids to evolve as next generation therapeutics. The current review is successive to our previously published review on drug delivery vehicles based on albumin-polymer conjugates and aims to provide an update on the progress of albumin-polymer conjugates. This review also highlights the alternative of exploring albumin-polymer conjugates formed via supramolecular, non-covalent interactions. Albumin-based supramolecular polymer systems provide a versatile platform for functionalization, thereby, holding great potential in enhancing cytotoxicity and controlled delivery of therapeutic agents.

Rational Design of Self-Assembling Supramolecular Protein Nanostructures Utilizing the Cucurbit[8]Uril Macrocyclic Host

Self-assembly is a phenomenon that governs molecular structural organization in nature, therefore raising research interest for the fabrication of novel nanomaterials with diverse applications in biocatalysis, biomedicine, material templating, and biosensor development. In this chapter we provide protocols for the development of supramolecular protein complexes based on host-guest interactions in the presence of the macrocyclic host, cucurbit[8]uril (CB[8]). CB[8] is reported to exhibit high binding affinity towards the tripeptide Phe-Gly-Gly (FGG), therefore it can be utilized as a selective adhesive of protein molecules, after fusion of FGG to an accessible protein surface.

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...

Affinity-Directed Dynamics of Host-Guest Motifs for Pharmacokinetic Modulation via Supramolecular PEGylation

Proteins are an impactful class of therapeutics but can exhibit suboptimal therapeutic performance, arising from poor control over the timescale of clearance. Covalent PEGylation is one established strategy to extend circulation time but often at the cost of reduced activity and increased immunogenicity. Supramolecular PEGylation may afford similar benefits without necessitating that the protein be permanently modified with a polymer. Here, we show that insulin pharmacokinetics can be modulated by tuning the affinity-directed dynamics of a host-guest motif used to non-covalently endow insulin with a poly(ethylene glycol) (PEG) chain. When administered subcutaneously, supramolecular PEGylation with higher binding affinities extends the time of total insulin exposure systemically. Pharmacokinetic modeling reveals that the extension in the duration of exposure arises specifically from decreased absorption from the subcutaneous depot governed directly by the affinity and dynamics of host-guest exchange. The lifetime of the supramolecular interaction thus dictates the rate of absorption, with negligible impact attributed to association of the PEG upon rapid dilution of the supramolecular complex in circulation. This modular approach to supramolecular PEGylation offers a powerful tool to tune protein pharmacokinetics in response to the needs of different disease applications.

Design and recognition of cucurbituril-secured platinum-bound oligopeptides

Platinum terpyridyl complexes, stacked on top of one another and secured as dimers with cucurbit[8]uril (CB[8]) in aqueous medium, were functionalized quantitatively and in situ with a pair of pentapeptides Phe-(Gly)₃-Cys by grafting their cysteine residues to the Pt centers. The resulting CB[8]·(Pt·peptide)₂ assemblies were used to target secondary hosts CB[7] and CB[8] via their pair of phenylalanine residues, again in situ. A series of well-defined architectures, including a supramolecular “pendant necklace” with hybrid head-to-head and head-to-tail arrangements inside CB[8], were obtained during the self-sorting process after combining only 3 or 4 simple building units.

A platinum terpyridyl complex, pentapeptide Phe-(Gly)₃-Cys and cucurbit[8]uril assemble into a “pendant necklace” with hybrid head-to-head and head-to-tail arrangements in aqueous medium.

A fluorescent probe based on cucurbit[7]uril for the selective recognition of phenylalanine

Herein we describe a simple fluorescence quenching method for the selective recognition and determination of the amino acid phenylalanine (Phe). The use of ¹H NMR spectroscopy revealed that the alkaloid palmatine (PAL) can encapsulated partially into the cavity of cucurbit[7]uril (Q[7]) in aqueous solution to form a stable 1:1 host-guest inclusion complex. This host-guest complex exhibits fluorescence of moderate intensity. Interestingly, the addition of the Phe results in a dramatic quenching of the fluorescence intensity associated with the inclusion complex. By contrast, the addition of other natural amino acids resulted in no change in the fluorescence. Based on the linear relationship between the fluorescence intensity and the concentration of Phe, the detection of the concentration of Phe in aqueous solution is facile. Thus, a new fluorescence quenching method for the recognition and determination of the Phe has established herein.

Reversible encapsulations and stimuli-responsive biological delivery from a dynamically assembled cucurbit[7]uril host and nanoparticle guest scaffold

The positive outcome of any therapeutic molecule requires control over its delivery rate. When delivered without control, administration of large doses is required to stimulate a therapeutic effect, frequently leading to increased toxicity or undesirable side effects. Recent advances introduced “smart” materials that actively release drugs in response to environmental stimuli. Although a variety of endogenous and exogenous triggers are reported, they are either difficult to control or lack tissue penetration depth. We report here a dynamic drug delivery scaffold based on a cucurbit[7]uril (CB[7]) host and benzylammonium functionalized gold nanoparticle (AuNP) guest that utilizes a bioorthogonal small molecule to achieve therapeutic control. In addition to their ability to reach deep tissue, small molecule activation is benefitted by their external controllability. Through cell culture studies we demonstrate that the host–guest supramolecular scaffold provides a nontoxic platform that effectively encapsulates a variety of therapeutic molecules and controls the payload release upon exposure to a high-affinity competitive guest molecule. This study presents a new strategy for controlling drug release rate through the use of competitive interactions of orthogonally presented guest molecules with immediate advantages in dosage control.

Cucurbit[8]uril-Based Polymers and Polymer Materials

Cucurbit[8]uril (CB[8]) is unique and notable in the cucurbit[n]uril family, since it has a relatively large cavity and thus is able to simultaneously accommodate two guest molecules. Typically, an electron-deficient first guest and an electron-rich second guest can be bound by CB[8] to form a stable 1:1:1 heteroternary supramolecular complex. Additionally, two homo guests can also be strongly dimerized inside the cavity of CB[8] to form a 2:1 homoternary supramolecular complex. During the past decade, by combining polymer science and CB[8] host-guest chemistry, a variety of systems have been established to construct supramolecular polymers with polymer chains typically at the nanoscale/sub-microscale, and CB[8]-based micro/nanostructured polymer materials in the form of polymer networks and hydrogels, microcapsules, micelles, vesicles, and colloidal particles, normally in solution and occasionally on surfaces. This Review summarizes the noncovalent interactions and strategies used for the preparation of CB[8]-based polymers and polymer materials with a focus on the representative and latest developments, followed by a brief discussion of their characterization, properties, and applications.

Fluorescent-Cavity Host: An Efficient Probe to Study Supramolecular Recognition Mechanisms

Using fluorometry to study the interactions between guests and host cavities is often challenging, especially for hosts with small cavities because the fluorophore may not be close to the binding site. Therefore, it is critical to overcome this hurdle to broaden the applicability of fluorometry in supramolecular chemistry. Herein, we designed a fluorescent-cavity host (H1) by conjugating the binding site of a pillar[5]arene cavity and studied its host-guest recognition mechanism in the cavity. Distinct fluorescent responses of H1 were observed for cyano homologues: the fluorescence was enhanced for succinonitrile but quenched for malononitrile. Such an unusual phenomenon with such subtle difference in guest structure was attributed to the different host-guest interactions induced by the subtle difference of guest locations within the H1 cavity. Our results indicate that developing fluorescent-cavity hosts as probes will provide a powerful and insightful way to explore the exquisite detail of host-guest recognition, self-assembly, and molecular machinery.

Injectable network biomaterials via molecular or colloidal self-assembly

Self-assembly is a powerful tool to create functional materials. A specific application for which self-assembled materials are ideally suited is in creating injectable biomaterials. Contrasting with traditional biomaterials that are implanted through surgical means, injecting biomaterials through the skin offers numerous advantages, expanding the scope and impact for biomaterials in medicine. In particular, self-assembled biomaterials prepared from molecular or colloidal interactions have been frequently explored. The strategies to create these materials are varied, taking advantage of engineered oligopeptides, proteins, and nanoparticles as well as affinity-mediated crosslinking of synthetic precursors. Self-assembled materials typically facilitate injectability through two different mechanisms: i) in situ self-assembly, whereby materials would be administered in a monomeric or oligomeric form and self-assemble in response to some physiologic stimulus, or ii) self-assembled materials that, by virtue of their dynamic, non-covalent interactions, shear-thin to facilitate flow within a syringe and subsequently self-heal into its reassembled material form at the injection site. Indeed, many classes of materials are capable of being injected using a combination of these two mechanisms. Particular utility has been noted for self-assembled biomaterials in the context of tissue engineering, regenerative medicine, drug delivery, and immunoengineering. Given the controlled and multifunctional nature of many self-assembled materials demonstrated to date, we project a future where injectable self-assembled biomaterials afford improved practice in advancing healthcare.

Fabrication of Polymer-Protein Hybrids

Rapid developments in organic chemistry and polymer chemistry promote the synthesis of polymer-protein hybrids with different structures and biofunctionalities. In this feature article, recent progress achieved in the synthesis of polymer-protein conjugates, protein-nanoparticle core-shell structures, and polymer-protein nanogels/hydrogels is briefly reviewed. The polymer-protein conjugates can be synthesized by the "grafting-to" or the "grafting-from" approach. In this article, different coupling reactions and polymerization methods used in the synthesis of bioconjugates are reviewed. Protein molecules can be immobilized on the surfaces of nanoparticles by covalent or noncovalent linkages. The specific interactions and chemical reactions employed in the synthesis of core-shell structures are discussed. Finally, a general introduction to the synthesis of environmentally responsive polymer-protein nanogels/hydrogels by chemical cross-linking reactions or molecular recognition is provided.

Photo-induced interfacial electron transfer of ZnO nanocrystals to control supramolecular assembly in water

Herein, we show how the inherent light-induced redox properties of semiconducting nanocrystals (NCs) can be utilized for the photo-driven reversible modulation of dynamic supramolecular systems formed at their interfaces that, on their own, do not respond to light. This was achieved by the unprecedented combination of photoactive zinc oxide NCs (ZnO NCs) with a host-guest chemistry of cucurbit[8]uril (CB[8]) providing a route to the semiconductor-assisted light modulation of supramolecular assemblies (SALSA), here mediated by the photo-generation of viologen radical cations (MV˙⁺) at the NC corona and their further dimerization enhanced by CB[8] macrocycles. The reported SALSA strategy was successfully applied for light-controlled reversible assembly processes at NC interfaces enabling light-triggered release of guest molecules from surface confined discrete CB[8] host-guest complexes.

Decoupled Associative and Dissociative Processes in Strong yet Highly Dynamic Host-Guest Complexes

Kinetics and thermodynamics in supramolecular systems are intimately linked, yet both are independently important for application in sensing assays and stimuli-responsive switching/self-healing of materials. Host-guest interactions are of particular interest in many water-based materials, sensing, and drug delivery applications. Herein we investigate the binding dynamics of a variety of electron-rich aromatic moieties forming hetero-ternary complexes with the macrocycle cucurbit[8]uril (CB[8]) and an auxiliary guest, dimethyl viologen, with high selectivity and equilibrium binding constants (K_eq up to 10¹⁴ M^-2). Using stopped-flow spectrofluorimetry, association rate constants were observed to approach the diffusion limit and were found to be insensitive to the structure of the guest. Conversely, the dissociation rate constants of the ternary complexes varied dramatically with the guest structure and were correlated with the thermodynamic binding selectivity. Hence differing molecular features were found to contribute to the associative and dissociative processes, mimicking naturally occurring reactions and giving rise to a decoupling of these kinetic parameters. Moreover, we demonstrate the ability to exploit these phenomena and selectively perturb the associative process with external stimuli (e.g., viscosity and pressure). Significantly, these complexes exhibit increased binding equilibria with increasing pressure, with important implications for the application of the CB[8] ternary complex for the formation of hydrogels, as these gels exhibit unprecedented pressure-insensitive rheological properties. A high degree of flexibility therefore exists in the design of host-guest systems with tunable kinetic and thermodynamic parameters for tailor-made applications across a broad range of fields.

Fluorescent Supramolecular Polymeric Materials

Fluorescent supramolecular polymeric materials are rising stars in the field of fluorescent materials not only because of the inherent optoelectronic properties originating from their chromophores, but also due to the fascinating stimuli-responsiveness and reversibility coming from their noncovalent connections. Especially, these noncovalent connections influence the fluorescence properties of the chromophores because their state of aggregation and energy transfer can be regulated by the assembly-disassembly process. Considering these unique properties, fluorescent supramolecular polymeric materials have facilitated the evolution of new materials useful for applications in fluorescent sensors, probes, as imaging agents in biological systems, light-emitting diodes, and organic electronic devices. In this Review, fluorescent supramolecular polymeric materials are classified depending on the types of main driving forces for supramolecular polymerization, including multiple hydrogen bonding, electrostatic interactions, π-π stacking interactions, metal-coordination, van der Waals interactions and host-guest interactions. Through the summary of the studies about fluorescent supramolecular polymeric materials, the status quo of this research field is assessed. Based on existing challenges, directions for the future development of this field are furnished.

Near-Quantitative Aqueous Synthesis of Rotaxanes via Bioconjugation to Oligopeptides and Proteins

In spite of widespread interest in rotaxane-based molecular machines and materials, rotaxanes have not been attached covalently to proteins. We describe the near-quantitative aqueous synthesis of [2]rotaxanes based on neutral and charged aqueous hosts-cucurbit[7]uril (CB7) and cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺), respectively-using the thiol-ene addition of cysteine and maleimide as a stoppering protocol. After verifying the high efficiency of the reaction using glutathione (GSH) as an oligopeptide stopper, we have employed cytochrome C (CytC) as a protein stopper to produce the first well-characterized protein-rotaxane bioconjugates. We anticipate that this methodology will enable the preparation of novel materials that combine the unique properties of proteins and mechanical bonds.

Selective, non-covalent conjugation of synthetic peptides with recombinant proteins mediated by host-guest chemistry

The combination of potent chemical moieties with biologically active proteins is key to some of today's most innovative therapeutic drugs. In order to obviate any chemical modification of the proteins, we present a novel and powerful strategy for the selective conjugation of recombinant protein domains with synthetically derived peptides via a cucurbit[8]uril host-guest chemistry approach.

Protein–polymer conjugates prepared via host–guest interactions: effects of the conjugation site, polymer type and molecular weight on protein activity

Protein–polymer conjugates are prepared via host–guest interactions and the effects of various parameters on protein activity are investigated.

PGMA-based supramolecular hyperbranched polycations for gene delivery

PGMA-based supramolecular hyperbranched polycations were synthesized for effective gene delivery.

Supramolecular free radicals: near-infrared organic materials with enhanced photothermal conversion

A novel kind of supramolecular free radical with significantly improved free radical yield and enhanced near-infrared (NIR) photothermal conversion has been fabricated. Perylene diimide (PDI) can undergo chemical reduction to generate PDI radical anions. Cucurbit[7]uril (CB[7]), a bulky hydrophilic head, was utilized to encapsulate the two end groups of the PDI derivative via host-guest interactions, thus hindering its aggregation and suppressing the dimerization and quenching of PDI radical anions in aqueous solution. Due to the increased concentration of radical anions and their absorption above 800 nm, the efficiency of NIR photothermal conversion was significantly improved. Compared with free radicals fabricated by covalent chemistry, the supramolecular free radicals established here could provide a facile approach for the promoted formation of aromatic free radicals, thus opening up a new strategy for the design of NIR photothermal materials with enhanced photothermal conversion.

The construction of supramolecular polymers through anion bridging: from frustrated hydrogen-bonding networks to well-ordered linear arrays

The construction of supramolecular polymers has been realized by converting random hydrogen-bonding networks into well-ordered linear hydrogen-bonding arrays through an anion-bridging strategy.

Protein–polymer therapeutics: a macromolecular perspective

The development of protein–polymer hybrids emerged several decades ago with the vision that their synergistic combination will offer macromolecular hybrids with manifold features to succeed as the next generation therapeutics.

Dual self-sorting by cucurbit[8]uril to transform a mixed micelle to vesicle

A systematic study on the cucurbit[8]uril (CB[8]) assisted transformation of a mixed micellar system of CTAB and a viologen surfactant to vesicles is depicted. The micelle to vesicle transformation is assisted by a charge transfer complex mediated ternary complexation between the viologen group of the surfactant, CB[8], and 2,6-dihydroxynaphthalene. In the presence of CB[8], both the surfactants formed U-shaped binary inclusion complexes inside the CB[8] cavity, and no selective binding is observed. Upon addition of DHN, CB[8] showed two different self-sorting mechanisms. The U-shaped binary complex with CTAB breaks down, and CB[8] moves toward the viologen headgroup of the other surfactant to form a stable ternary complex. In the case of the viologen surfactant, CB[8] moved toward the headgroup leaving the hydrophobic tail free in order to form the ternary complex. The mechanistic detail of this micelle to vesicle transformation is revealed through methodical studies using (1)H and DOSY NMR, ESI-MS, ITC, and other instrumental techniques.

Covalent bond or noncovalent bond: a supramolecular strategy for the construction of chemically synthesized vaccines

A novel noncovalent strategy to construct chemically synthesized vaccines has been designed to trigger a robust immune response and to dramatically improve the efficiency of vaccine preparation. Glycosylated MUC1 tripartite vaccines were constructed through host-guest interactions with cucurbit[8]uril. These vaccines elicited high levels of IgG antibodies that were recognized by transformed cells and induced the secretion of cytokines. The antisera also mediated complement-dependent cytotoxicity. This noncovalent strategy with good suitability, scalability, and feasibility can be applied as a universal strategy for the construction of chemically synthesized vaccines.