Drastic Stabilization of Junction Nodes in Supramolecular Structures Based on Host–Guest Complexes

Theoretical prediction of nanomolar and sequence-selective binding of synthetic supramolecular cucurbit[7]uril to N-terminal Leu-containing tripeptides

Molecular recognition towards peptides and proteins with high affinity by synthetic supramolecular hosts is important but challenging. In this work, we investigate the molecular recognition of the synthetic cucurbit[7]uril (CB[7]) to 17 designed N-terminal Leu-containing tripeptides in aqueous medium by molecular dynamics (MD) simulation and screen out tripeptides with high binding affinity. It is found that, compared to LGG, only the third residue is Arg (R), the binding affinity of CB[7] to LGR reaches nanomolar level with binding equilibrium constant (K_a) of 1.1 × 10⁹ M^-1. The CB[7] recognition to the N-terminal Leu-containing tripeptides is highly sequence dependent; whether changing the sequence order (from LGR to LRG) or increasing the sequence length (from LGR to LGGR), K_a decreases by about three orders of magnitude. Interestingly, substituting N-terminal Leu for its isomer Ile, the binding of CB[7] to tripeptides weakens significantly with K_a decreasing by 3-8 orders of magnitude. Thus CB[7] can effectively distinguish N-terminal Leu-containing tripeptides from N-terminal Ile-containing tripeptides. Importantly, we predict that when R is as C-terminus, regardless of N-terminal residue being of aromatic type or Leu, the binding strength is always close to the nanomolar level. Therefore, R can be introduced to rationally design novel peptides with high binding affinity to CB[7] in practical applications.

Size compatibility and concentration dependent supramolecular host-guest interactions at interfaces

The quantification of supramolecular host-guest interactions is important for finely modulating supramolecular systems. Previously, most host-guest interactions quantified using force spectroscopic techniques have been reported in force units. However, accurately evaluating the adhesion energies of host-guest pairs remains challenging. Herein, using a surface forces apparatus, we directly quantify the interaction energies between cyclodextrin (CD)-modified surfaces and ditopic adamantane (DAd) molecules in water as a function of the DAd concentration and the CD cavity size. The adhesion energy of the β-CD-DAd complex drastically increased with increasing DAd concentration and reached saturation. Moreover, the molecular adhesion energy of a single host-guest inclusion complex was evaluated to be ~9.51 kBT. This approach has potential for quantifying fundamental information toward furthering the understanding of supramolecular chemistry and its applications, such as molecular actuators, underwater adhesives, and biosensors, which require precise tuning of specific host-guest interactions.

Sequence-selective recognition of cationic amphipathic tripeptides with similar structures in aqueous solutions by cucurbit[7]uril

Sequence-selective recognition of cationic amphipathic peptides by synthetic receptors is significant to biological applications, but it is still a great challenging task. Here we first study the binding characteristics of receptor cucurbit[7]uril (CB[7]) to the smallest aromatic tripeptides X1GG (X1 = tryptophan (W), phenylalanine (F), and tyrosine (Y)) and basic tripeptides X2GG (X2 = arginine (R), lysine (K), and histidine (H)) by molecular dynamics simulations. The study indicates that the sidechains of aromatic X1 residues can be encapsulated into the CB[7] cavity, while the sidechains of basic X2 residues prefer to locate at the CB[7] portal. Based on that, we consider hydrophobic aromatic residues as the N-terminus, the smallest glycine (G) as the 2nd-residue and basic residues as the C-terminus, and design nine tripeptides X1GX2 (X1 = F, Y, W and X2 = H, K, R). We found that there is a great influence of the C-terminal basic residue of X1GX2 on binding with CB[7] due to the introduction of a new binding site between CB[7] and the sidechain of the C-terminal residue. Interestingly, CB[7] can differentiate WGR and WGK with similar structures efficiently because of their eight orders of magnitude difference in the association constant (Ka). Besides, for WGR, YGR, and YGK with a nanomolar binding affinity (Ka > 109 M-1), on reversing the sequence order of the 2nd-residue and 3rd-residue, their Ka reduces by about at least 1000-fold, implying the sequence dependence of CB[7] on recognizing these tripeptides. These results predict the potential applications of CB[7] in recognizing cationic amphipathic peptides.

Molecular insight into COF monolayers for urea sorption in artificial kidneys

Urea removal from an aqueous solution is considered a challenge in the biological process. The state of complete kidney destruction is known as an end-stage renal disease (ESRD). Kidney transplant and hemodialysis are the most common methods for confronting ESRD. More recently, wearable artificial kidney (WAK) devices have shown a significant improvement in urea removal performance. However, low efficiency in physical adsorbents is a barrier in developing them. For the first time, the urea adsorption capacity of five types of last-generation covalent organic framework (COF) nanosheets (NSs) was investigated in this study by applying molecular dynamics (MD) simulation tools. To this end, different analyses have been performed to evaluate the performance of each nanoparticle. The MD all-atom (AA) results demonstrated that all introduced COF NSs had urea removal capacity. Among the five NSs, TPA-COF was shown to have the best outcomes. Moreover, coarse-grained (CG) and density functional theory (DFT) simulations were conducted, and the results show that the TPA-COF nanoparticle modified with -OH functional group has even better properties for urea adsorption. The present molecular study sheds new light on COF NSs as an adsorbent for urea removal.

Cyclodextrin Polymers and Cyclodextrin-Containing Polysaccharides for Water Remediation

Chemical pollution of water has raised great concerns among citizens, lawmakers, and nearly all manufacturing industries. As the legislation addressing liquid effluents becomes more stringent, water companies are increasingly scrutinized for their environmental performance. In this context, emergent contaminants represent a major challenge, and the remediation of water bodies and wastewater demands alternative sorbent materials. One of the most promising adsorbing materials for micropolluted water environments involves cyclodextrin (CD) polymers and cyclodextrin-containing polysaccharides. Although cyclodextrins are water-soluble and, thus, unusable as adsorbents in aqueous media, they can be feasibly polymerized by using different crosslinkers such as epichlorohydrin, polycarboxylic acids, and glutaraldehyde. Likewise, with those coupling agents or after substituting hydroxyl groups with more reactive moieties, cyclodextrin units can be covalently attached to a pre-existing polysaccharide. In this direction, the functionalization of chitosan, cellulose, carboxymethyl cellulose, and other carbohydrate polymers with CDs is vastly found in the literature. For the system containing CDs to be used for remediation purposes, there are benefits from a synergy that arises from (i) the ability of CD units to interact selectively with a broad spectrum of molecules, forming inclusion complexes and higher-order supramolecular assemblies, (ii) the functional groups of the crosslinker comonomers, (iii) the three-dimensional structure of the crosslinked network, and/or (iv) the intrinsic characteristics of the polysaccharide backbone. In view of the most recent contributions regarding CD-based copolymers and CD-containing polysaccharides, this review discusses their performance as adsorbents in micropolluted water environments, as well as their interaction patterns, addressing the influence of their structural and physicochemical properties and their functionalization.

Theoretical design of an ultrafast supramolecular rotor composed of carbon nano-rings

A new type of supramolecular rotor composed of C₁₈ and cycloparaphenylenes exhibits ultrahigh rotation speeds as temperature increases.

Cyclodextrin-Based Multistimuli-Responsive Supramolecular Assemblies and Their Biological Functions

Cyclodextrins (CDs), which are a class of cyclic oligosaccharides extracted from the enzymatic degradation of starch, are often utilized in molecular recognition and assembly constructs, primarily via host-guest interactions in water. In this review, recent progress in CD-based supramolecular nanoassemblies that are sensitive to chemical, biological, and physical stimuli is updated and reviewed, and intriguing examples of the biological functions of these nanoassemblies are presented, including pH- and redox-responsive drug and gene delivery, enzyme-activated specific cargo release, photoswitchable morphological interconversion, microtubular aggregation, and cell-cell communication, as well as a geomagnetism-controlled nanosystem for the suppression of tumor invasion and metastasis. Moreover, future perspectives and challenges in the fabrication of intelligent CD-based biofunctional materials are also discussed at the end of this review, which is expected to promote the translational development of these nanomaterials in the biomedical field.

Complex systems that incorporate cyclodextrins to get materials for some specific applications

Cyclodextrins (CDs) are a family of biodegradable cyclic hydrocarbons composed of α-(1,4) linked glucopyranose subunits, the more common containing 6, 7 or 8 glucose units are named α, β and γ-cyclodextrins respectively. Since the discovery of CDs, they have attracted interest among scientists and the first studies were about the properties of the native compounds and in particular their use as catalysts of organic reactions. Characteristics features of different types of cyclodextrins stimulated investigation in different areas of research, due to its non-toxic and non-inmunogenic properties and also to the development of an improved industrial production. In this way, many materials with important properties have been developed. This mini-review will focus on chemical systems that use cyclodextrins, whatever linked covalently or mediated by the non covalent interactions, to build complex systems developed mainly during the last five years.

Hydrogel-Based Drug Delivery Nanosystems for the Treatment of Brain Tumors

Chemotherapy is commonly associated with limited effectiveness and unwanted side effects in normal cells and tissues, due to the lack of specificity of therapeutic agents to cancer cells when systemically administered. In brain tumors, the existence of both physiological barriers that protect tumor cells and complex resistance mechanisms to anticancer drugs are additional obstacles that hamper a successful course of chemotherapy, thus resulting in high treatment failure rates. Several potential surrogate therapies have been developed so far. In this context, hydrogel-based systems incorporating nanostructured drug delivery systems (DDS) and hydrogel nanoparticles, also denoted nanogels, have arisen as a more effective and safer strategy than conventional chemotherapeutic regimens. The former, as a local delivery approach, have the ability to confine the release of anticancer drugs near tumor cells over a long period of time, without compromising healthy cells and tissues. Yet, the latter may be systemically administered and provide both loading and targeting properties in their own framework, thus identifying and efficiently killing tumor cells. Overall, this review focuses on the application of hydrogel matrices containing nanostructured DDS and hydrogel nanoparticles as potential and promising strategies for the treatment and diagnosis of glioblastoma and other types of brain cancer. Some aspects pertaining to computational studies are finally addressed.

Combining Cellulose and Cyclodextrins: Fascinating Designs for Materials and Pharmaceutics

Cellulose and cyclodextrins possess unique properties that can be tailored, combined, and used in a considerable number of applications, including textiles, coatings, sensors, and drug delivery systems. Successfully structuring and applying cellulose and cyclodextrins conjugates requires a deep understanding of the relation between structural, and soft matter behavior, materials, energy, and function. This review focuses on the key advances in developing materials based on these conjugates. Relevant aspects regarding structural variations, methods of synthesis, processing and functionalization, and corresponding supramolecular properties are presented. The use of cellulose/cyclodextrin conjugates as intelligent platforms for applications in materials science and pharmaceutical technology is also outlined, focusing on drug delivery, textiles, and sensors.