Cucurbituril: A promising organic building block for the design of coordination compounds and beyond

Density Functional Theory Prediction of Laser Dyes-Cucurbit[7]uril Binding Affinities

Among a variety of diverse host molecules distinguished by specific characteristics, the cucurbit[n]uril (CB) family stands out, being widely known for the attractive properties of its representatives along with their increasingly expanding area of applications. The presented herewith density functional theory (DFT)-based study is inspired by some recent studies exploring CBs as a key component in multifunctional hydrogels with applications in materials science, thus considering CB-assisted supramolecular polymeric hydrogels (CB-SPHs), a new class of 3D cross-linked polymer materials. The research systematically investigates the inclusion process between the most applied representative of the cavitand family CB[7] and a series of laser dye molecules as guests, as well as the possible encapsulation of a model side chain from the photoanisotropic polymer PAZO and its sodium-containing salt. The obtained results shed light on the most significant factors that play a key role in the recognition process, such as binding mode, charge, and dielectric constant of the solvent. The observed findings provide valuable insights at a molecular level for the design of dye-CB[7] systems in various environments, with potential applications in intriguing and prosperous fields like photonics and material science.

A Review of Macrocycles Applied in Electrochemical Energy Storge and Conversion

Macrocycles composed of diverse aromatic or nonaromatic structures, such as cyclodextrins (CDs), calixarenes (CAs), cucurbiturils (CBs), and pillararenes (PAs), have garnered significant attention due to their inherent advantages of possessing cavity structures, unique functional groups, and facile modification. Due to these distinctive features enabling them to facilitate ion insertion and extraction, form crosslinked porous structures, offer multiple redox-active sites, and engage in host-guest interactions, macrocycles have made huge contributions to electrochemical energy storage and conversion (EES/EEC). Here, we have summarized the recent advancements and challenges in the utilization of CDs, CAs, CBs, and PAs as well as other novel macrocycles applied in EES/EEC devices. The molecular structure, properties, and modification strategies are discussed along with the corresponding energy density, specific capacity, and cycling life properties in detail. Finally, crucial limitations and future research directions pertaining to these macrocycles in electrochemical energy storage and conversion are addressed. It is hoped that this review is able to inspire interest and enthusiasm in researchers to investigate macrocycles and promote their applications in EES/EEC.

Cucurbit[8]uril-based supramolecular theranostics

Different from most of the conventional platforms with dissatisfactory theranostic capabilities, supramolecular nanotheranostic systems have unparalleled advantages via the artful combination of supramolecular chemistry and nanotechnology. Benefiting from the tunable stimuli-responsiveness and compatible hierarchical organization, host-guest interactions have developed into the most popular mainstay for constructing supramolecular nanoplatforms. Characterized by the strong and diverse complexation property, cucurbit[8]uril (CB[8]) shows great potential as important building blocks for supramolecular theranostic systems. In this review, we summarize the recent progress of CB[8]-based supramolecular theranostics regarding the design, manufacture and theranostic mechanism. Meanwhile, the current limitations and corresponding reasonable solutions as well as the potential future development are also discussed.

Cycloglycolurils: Hybrid Glycoluril-Cyclobenzil Macrocycles

Two novel glycoluril macrocycles have been synthesized from cyclotetrabenzil and cyclotribenzoin precursors using solvent-free condensations with urea. The crystal structure of the cyclotetra(p-phenylene)glycoluril macrocycle shows a twisted ring conformation, while that of the cyclotri(m-phenylene)glycoluril hybrid exhibits a distinct tubular supramolecular packing. These structures establish a potentially broad new class of macrocycles with intriguing guest binding properties owing to their available N-H motifs.

Electrochemiluminescence of an iridium complex doped with SiO2 nanoparticles to detect 2-adamantanamine based on the host-guest interaction of cucurbit[7]uril

The poor solubility of iridium complexes severely hampers its application in the electrochemiluminescence (ECL) sensing field. The doping of an iridium complex with silica (SiO2) nanospheres provides feasible solution for this problem. Herein, one kind of water insoluble iridium complex ([Ir(dFppy)2(d(CF3)bpy)](PF6)) was doped with SiO2 nanoparticles to obtain a luminescent nanocomposite (SiO2@Ir) which could generate strong ECL signals to act as a beacon molecule. An "off-on-off" mode ECL sensor was proposed based on the competitive host-guest interactions between 2-adamantanamine (2-ADA), ferrocene (Fc) and cucurbit[7]uril (Q[7]). Fc could be used as an inhibitor to decrease the ECL signal, while Q[7] could wrap Fc to recover the ECL signal. Q[7] has a stronger binding ability with 2-ADA than Fc. As a result, 2-ADA could replace Fc from the cavity of Q[7], and the ECL signal was inhibited again. Under the optimal conditions, the ECL intensity varied linearly with 2-ADA concentration in the range of 1.0 × 10-8 to 1.0 × 10-6 mol L-1 with a detection limit of 2.5 × 10-10 mol L-1. The results not only provided a new avenue for the application of water insoluble iridium complexes in ECL sensing, but also revealed the attractive potential of host-guest interactions in the fabrication of biosensors.

N-Methyl- and N-Phenylpiperazine Functionalized Styryl Dyes Inside Cucurbiturils: Theoretical Assessment of the Factors Governing the Host-Guest Recognition

The family of cucurbiturils (CBs), the unique pumpkin-shaped macrocycles, has received great attention over the past four decades owing to their remarkable recognition properties. They have found diverse applications including biosensing and drug delivery technologies. The cucurbituril complexation of guest molecules can modulate their pKas, improve their solubility in aqueous solution, and reduce the adverse effects of the drugs, as well as enhance the stability and/or enable targeted delivery of the drug molecule. Employing twelve cationic styryl dyes with N-methyl- and N-phenylpiperazine functionality as probes, we attempted to understand the factors that govern the host-guest complexation of such molecules within CB[7] and CB[8] host systems. Various key factors determining the process were recognized, such as the pH and dielectric constant of the medium, the cavity size of the host, the chemical characteristics of the substituents in the guest entity, and the presence/absence of metal cations. The presented results add to our understanding (at the molecular level) of the mechanism of encapsulation of styryl dyes by cucurbiturils, thus shedding new light on various aspects of the intriguing complexation chemistry and the underlying recognition processes.

Handcuff-like metallo-pseudorotaxanes consisting of tiara[5]arene wheels and dimeric silver trifluoroacetate axles

The complexation between tiara[5]arene (T[5]) and silver trifluoroacetate affords a binuclear metallo-pseudorotaxane on account of multiple endo-cavity Ag^I η²-arene interactions. Furthermore, two such enantiomeric [(CF₃CO₂Ag)₂⊂T[5]] complexes are bridged by an extra (CF₃CO₂Ag)₂ dimer through exo-wall Ag^I η²-arene coordination, resulting in a unique handcuff metallo-bis-pseudorotaxane structure in the solid state.

Construction of a supramolecular framework consisting of cucurbit[8]uril and 1-(4-methoxyphenyl)piperazine

We report the supramolecular self-assembly of cucurbit[8]uril(Q[8]) and 1-(4-methoxyphenyl)piperazine inclusion complex. The complex is cultured in 3 M hydrochloric acid solution under CdCl2 induction conditions to obtain a new crystal, the structure of which was characterized by X-ray single-crystal diffraction. The results show that the crystal belongs to the monoclinic crystal system with a C2/m space group. The host–guest interaction ratio of Q[8] and 1-(4-methoxyphenyl) piperazine is 1:2.

Optical Chemical Sensing of Iodide Ions: A Comprehensive Review for the Synthetic Strategies of Iodide Sensing Probes, Challenges, and Future Aspects

Among several anions, iodide (I^- ) ions play a crucial role in human biological activities. In it's molecular form (I₂ ), iodine is utilized for several industrial applications such as syntheses of medicines, fabric dyes, food additives, solar cell electrolytes, catalysts, and agrochemicals. The excess or deficiency of I^- ions in the human body and environmental samples have certain consequences. Therefore, the selective and sensitive detection of I^- ions in the human body and environment is vital for monitoring their overall profile. Amongst various analytical techniques for the estimation of I^- ions, optical-chemical sensing possesses the merits of high sensitivity, selectivity, and utilizing the least amount of sensing materials. The distinctive aims of this manuscript are (i) To comprehensively review the development of optical chemical sensors (fluorescent & colorimetric) reported between 2001-2021 using organic fluorescent molecules, supramolecular materials, conjugated polymers, and metal-organic frameworks (MOFs). (ii) To illustrate the design and synthetic strategies to create specific binding and high affinity of I^- ions which could help minimize negative consequences associated with its large size and high polarizability. (iii) The challenges associated with sensitivity and selectivity of I^- ions in aqueous and real samples. The probable future aspects concerning the optical chemical detection of I^- ions have also been discussed in detail.

Clustering emission of cucurbit[n]urils in the solid- and solution-state induced by the outer surface interactions of cucurbit[n]urils

Atypical luminescent compounds that do not contain conventional chromophores emit light due to clustering and have important basic research value and a broad range of potential applications. To date, most atypical luminescent compounds are small molecules or polymers containing groups such as cyano, carbonyl and hydroxyl. In this work, driven by some sporadic and accidental luminescence phenomena observed for cucurbit[n]urils (Q[n]s), the luminescent properties and mechanism of Q[n]s in the solid- and solution-state were systematically studied and the clustering emission of Q[n]s confirmed. Our experiments have revealed that the self-induced outer-surface interactions of Q[n]s (OSIQ) are the most important driving force resulting in the clustering emission of Q[n]s. Substances that can weaken the effect of self-induced OSIQ, such as the presence of various aromatic compounds and anions, may weaken or quench the clustering emission of Q[n]s. This not only reveals the new characteristics and mechanism of the clustering emission of Q[n]s, but also provides new insights on how to utilize the clustering emission of Q[n]s and construct new types of macrocyclic luminescence systems.

Hybrid Macrocyclic Polymers: Self-Assembly Containing Cucurbit[m]uril-pillar[n]arene

Supramolecular self-assembly by hybrid macrocycles containing both cucurbit[m]uril (CB[m]) and pillar[n]arene was discussed and summarized in this review. Due to different solubility, diverse-sized cavities, and various driving forces in recognizing guests, the role of CB[m] and pillar[n]arene in such hybrid macrocyclic systems could switch between competitor in capturing specialized guests, and cooperator for building advanced hybridized macrocycles, by controlling their characteristics in host-guest inclusions. Furthermore, both CB[m] and pillar[n]arene were employed for fabricating advanced supramolecular self-assemblies such as mechanically interlocked molecules and supramolecular polymers. In those self-assemblies, CB[m] and pillar[n]arene played significant roles in, e.g., microreactor for catalyzing particular reactions to bridge different small pieces together, molecular "joint" to connect different monomers into larger assemblies, and "stabilizer" in accommodating the guest molecules to adopt a favorite structure geometry ready for assembling.

Assembly and Applications of Macrocyclic-Confinement-Derived Supramolecular Organic Luminescent Emissions from Cucurbiturils

Cucurbit[n]urils (Q[n]s or CB[n]s), as a classical of artificial organic macrocyclic hosts, were found to have excellent advantages in the fabricating of tunable and smart organic luminescent materials in aqueous media and the solid state with high emitting efficiency under the rigid pumpkin-shaped structure-derived macrocyclic-confinement effect in recent years. This review aims to give a systematically up-to-date overview of the Q[n]-based supramolecular organic luminescent emissions from the confined spaces triggered host-guest complexes, including the assembly fashions and the mechanisms of the macrocycle-based luminescent complexes, as well as their applications. Finally, challenges and outlook are provided. Since this class of Q[n]-based supramolecular organic luminescent emissions, which have essentially derived from the cavity-dependent confinement effect and the resulting assembly fashions, emerged only a few years ago, we hope this review will provide valuable information for the further development of macrocycle-based light-emitting materials and other related research fields.

Complexation of trivalent metal cations (Al3+, Ga3+, In3+, La3+, Lu3+) to cucurbiturils: a DFT/SMD evaluation of the key factors governing the host-guest recognition

Cucurbiturils (CBs), the pumpkin-shaped macrocycles, are suitable hosts for an array of neutral and cationic species. A plethora of host-guest complexes between CBs and a variety of guest molecules has been studied. However, much remains unknown, even in the complexation of very simple guests such as metal cations. In the computational study herein, DFT molecular modeling has been employed to investigate the interactions of a series of trivalent metal cations (Al³⁺, Ga³⁺, In³⁺, La³⁺, Lu³⁺) to cucurbit[n]urils and to evaluate the main factors controlling the host-guest complexation. The thermodynamic descriptors (Gibbs energies in the gas phase and in a water environment) of the corresponding complexation reactions have been estimated. This research is a logical continuation of an earlier study on the interaction between CB[n]s and a series of biologically essential mono- and divalent metal cations (Na⁺/K⁺ and Mg²⁺/Ca²⁺, respectively).

Sensitive and selective detection of carbamazepine in serum samples by bionic double-antibody sandwich method based on cucurbit[7]uril and molecular imprinted polymers

A novel bionic enzyme-linked immunosorbent assay (BELISA) based on double-antibody sandwich method is firstly designed for the detection of carbamazepine (CBZ) in human serum samples. In this BELISA system, cucurbit[7]uril (CB[7]) is employed as an artificial capture antibody (cAb), and molecularly imprinted polymers (MIPs) is used as an artificial detection antibody (dAb). Nanozymes (PdNPs) as signal generators are integrated with MIPs. This couple of bionic antibodies exhibits not only the excellent physical and chemical stability, but also the superior molecular recognition ability. Based on two bionic antibodies that can selectively recognize different sites of CBZ molecule, a new BELISA method has been constructed for the first time. The proposed BELISA method displays a good linear relationship ranging from 2 to 20 μg mL^-1. The detection limit is 0.37 μg mL^-1, which can well meet clinical testing demand. It provides a more stable and economical method for clinical therapeutic drug monitoring (TDM).

Construction of cucurbit[n]uril-based supramolecular frameworks via host-guest inclusion and functional properties thereof

Frameworks utilizing cucurbit[n]uril-based chemistry build on the rapid developments in the fields of metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and supramolecular organic frameworks (SOFs), and as porous materials have found...

"Turn-Off" Supramolecular Fluorescence Array Sensor for Heavy Metal Ion Identification

A "turn-off" supramolecular fluorescence array sensor based on the host-guest complexes between fluorescence dyes and cucurbit[n]urils for sensing metal ions was developed. Three fluorescent probes (RhB@Q[7], H33342@2Q[7], and BRE@Q[7]) were used as the sensing units to construct a supramolecular fluorescence array sensor. The binding ability of the metal ions and cucurbituril-dye probes varied; therefore, the probes and metal ions produced different fluorescence responses. When combined with linear discriminant analysis (LDA), the qualitative and quantitative detection of seven metal ions was achieved. In analytical samples, the supramolecular fluorescence array sensor recognized and distinguish seven metal ions. These results provided new research ideas for the rapid analysis and real-time monitoring of different heavy metal ions.

Multiple Stimuli-Responsive Supramolecular Hydrogels Constructed by Decamethylcucurbit[5]uril-para-phenylenediamine Exclusion Complex

The hydrogels composed of decamethylcucurbit[5]uril (Me₁₀ Q[5]) and para-phenylenediamine (p-PDA) are first reported herein. They are the first Q[5]-based supramolecular hydrogels, the formation of which is driven by portal exclusion between Me₁₀ Q[5] and p-PDA. The composition, structure, and properties of the Me₁₀ Q[5]/p-PDA-based hydrogels are investigated by various techniques. Since the 1D supramolecular chain forms via portal exclusion between Me₁₀ Q[5] and p-PDA is the key to the formation of the hydrogels, any competitive species, such as metal ions, organic molecules, and amino acids, which can affect the portal exclusion, can change the behavior of the Me₁₀ Q[5]/p-PDA-based hydrogels. Hence, the hydrogels can be used for various applications. Importantly, the results may provide a new research direction for the preparation of Q[n]-based hydrogels via portal exclusion of Q[n]s with guests.

Selective Separation of Hexachloroplatinate(IV) Dianions Based on Exo-Binding with Cucurbit[6]uril

The recognition and separation of anions attracts attention from chemists, materials scientists, and engineers. Employing exo-binding of artificial macrocycles to selectively recognize anions remains a challenge in supramolecular chemistry. We report the instantaneous co-crystallization and concomitant co-precipitation between [PtCl₆ ]^2- dianions and cucurbit[6]uril, which relies on the selective recognition of these dianions through noncovalent bonding interactions on the outer surface of cucurbit[6]uril. The selective [PtCl₆ ]^2- dianion recognition is driven by weak [Pt-Cl⋅⋅⋅H-C] hydrogen bonding and [Pt-Cl⋅⋅⋅C=O] ion-dipole interactions. The synthetic protocol is highly selective. Recognition is not observed in combinations between cucurbit[6]uril and six other Pt- and Pd- or Rh-based chloride anions. We also demonstrated that cucurbit[6]uril is able to separate selectively [PtCl₆ ]^2- dianions from a mixture of [PtCl₆ ]^2- , [PdCl₄ ]^2- , and [RhCl₆ ]^3- anions. This protocol could be exploited to recover platinum from spent vehicular three-way catalytic converters and other platinum-bearing metal waste.

Alkali and alkaline earth coordination polymers constructed from benzene-1,2,4,5-tetracarboxylic acid and flexible dicarboxylate acid ligands: syntheses, structures and spectroscopic and thermal properties

Two new metal coordination complexes, namely, poly[aqua(μ₆-benzene-1,2,4,5-tetracarboxylic acid-κ⁸O¹:O¹,O²:O^2':O⁴:O⁴,O⁵:O^5')(μ-but-2-enedioato-κ²O¹:O⁴)potassium(I)], [K₂(C₄H₂O₄)(C₁₀H₆O₈)(H₂O)₂]_n or [K₂(fum)(H₄btec)(H₂O)₂]_n, (1), and poly[aqua(μ₈-2,5-dicarboxybenzene-1,4-dicarboxylato-κ¹²O¹:O^1',O²:O²,O^2':O^2':O⁴:O^4',O⁵:O⁵,O^5':O^5')(μ-ethanedioato-κ⁴O¹,O²:O^1',O^2')strontium(II)], [Sr₂(C₂O₄)(C₁₀H₄O₈)(H₂O)₂]_n or [Sr₂(ox)(H₂btec)(H₂O)₂]_n, (2) (H₄btec = benzene-1,2,4,5-tetracarboxylic acid, H₂btec = 2,5-dicarboxybenzene-1,4-dicarboxylate, fum = fumarate and ox = oxalate), have been obtained under hydrothermal conditions by reacting the different alkali and alkaline earth metal salts with H₄btec, fumaric acid (H₂fum) and oxalic acid (H₂ox). Complexes (1) and (2) were structurally characterized by single-crystal X-ray diffraction, IR and UV-Vis spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetic analysis-differential scanning calorimetry (TGA-DSC). Complex (1) displays a two-dimensional (2D) layer with the K⁺ ion in a distorted pentagonal bipyramidal geometry and exhibits a uninodal 6-connected hxl/Shubnikov plane net (3,6) with {3⁶.4⁶.5³} topology. Complex (2) displays a three-dimensional (3D) network structure, in which the Sr²⁺ ion is in a distorted monocapped square antiprism geometry. The framework possess a binodal (5,8)-connected net with the Schläfli symbol {3².4¹⁰.5⁸.6⁴.7⁴}{3².4⁶.5²}₂. The 3D Hirshfeld surfaces and 2D fingerprint plots show that the main interactions are the O...H/H...O intermolecular interactions. Moreover, the thermal decompositions of (1) and (2) in the temperature range 303-1273 K revealed that they both decompose in three steps and transform to the corresponding metal oxide.

Cucurbit[n]uril-Based Supramolecular Frameworks Assembled through Outer-Surface Interactions

Porous materials, especially metal-organic frameworks, covalent organic frameworks, and supramolecular organic frameworks, are widely used in heterogeneous catalysis, adsorption, and ion exchange. Cucurbit[n]urils (Q[n]s) suitable building units for porous materials because they possess cavities with neutral electrostatic potential, portal carbonyls with negative electrostatic potential, and outer surfaces with positive electrostatic potential, which may result in the formation of Q[n]-based supramolecular frameworks (QSFs) assembled through the interaction of guests within Q[n]s, the coordination of Q[n]s with metal ions, and outer-surface interaction of Q[n]s (OSIQ). This review summarizes the various QSFs assembled via OSIQs. The QSFs can be classified as being assembled by 1) self-induced OSIQ, 2) anion-induced OSIQ, and 3) aromatic-induced OSIQ. The design and construction of QSFs with novel structures and specific functional properties may establish a new research direction in Q[n] chemistry.

Host-guest modes and supramolecular frameworks of complexes of tetramethyl cucurbit[6]uril with 4-chloroaniline and 4,4'-diaminostilbene

Since the first reportal on decamethylcucurbit[5]uril (Me10Q[5]) in 1992, substituted cucurbit[n]urils have attracted considerable research interest. In this study, the host-guest modes between the tetramethyl cucurbit[6]uril (TMeQ[6]) as a host and 4-chloroaniline and 4,4'-diaminostilbene (G1 and G2) as guests were investigated by single-crystal X-ray diffraction, NMR, ITC, UV-Vis spectrum, and MALDI-TOF mass spectrometry analyses. The experimental results showed that TMeQ[6] formed a 1 : 1 inclusion compound with G1, and the carbonyl portal of TMeQ[6] formed a 1 : 1 self-assembly with G2. Further, multi-dimensional supramolecular frameworks were formed driven by weak interaction forces in the system (hydrogen bonding, C-H⋯π interactions, ion-dipole interactions, and dipole-dipole interactions).

Cucurbituril-Oriented Nanoplatforms in Biomedical Applications

Cucucrbituril (CB) belongs to a family of macrocycles that are easily accessible. Their structural specificity provides excellent molecular recognition capabilities, with the ability to be readily chemically modified. Because of these properties, researchers have found CB to be a useful molecular carrier for delivering drug molecules and therapeutic biomolecules. Their significance lies in the fact that CB not only increases the solubility and stability of an encapsulated guest but also provides the possibility to achieve targeted delivery of the guest molecule. Therefore, the emergence of CB undoubtedly provides opportunities for the development of targeted drug delivery in an era where intelligent drugs have attracted considerable attention. It has also been found that CB can enhance fluorescent dyes, allowing the preparation of biosensors with enhanced sensitivity for use in clinical settings. In the present review, the acquisition, properties, and structural modifications of CB are first comprehensively described, and then the value of this macrocycle in applications within the medical field is discussed. In addition, we have also summarized patent applications of CB in this field over recent years, aiming to illustrate the current status of developments of this molecule. Finally, we discuss the challenges faced by CB in the medical field and future trends in its development.

Separating Enthalpic, Configurational, and Solvation Entropic Components in Host-Guest Binding: Application to Cucurbit[7]uril Complexes through a Full In Silico Approach via Water Nanodroplets

Cucurbiturils are a family of supramolecular hosts obtained by condensation of glycoluril and formaldehyde. Cucurbit[7]uril, CB[7], is the most prominent member of the family for its biomolecular interest, arising from its mild solubility in water and for its strong binding with a large variety of guests containing nonpolar fragments such as adamantanes and ferrocene. For instance, CB[7] encapsulates diamantane diammonium iodide with an attomolar dissociation constant, a value unmatched even in natural encapsulation processes. Computational chemistry has been extensively employed to describe the enthalpic-entropic compensation principle of the molecular recognition process of cucurbituril hosts, but the synergistic contribution of experimental data is required for accurate results to be obtained. This paper proposes the first fully theoretical model able to reconcile the calculated thermodynamics of the complexation process with the experimental data obtained by calorimetry (ITC) for cucurbit[7]uril. The model allows the isolation and estimation of all of the enthalpic and entropic contributions coming from solute and solvent alike to the whole host-guest binding event and enables the straightforward calculation of the contribution of the solvation entropy to the binding.

Cucurbiturils regulating Fe3O4-Au nanoparticles as a multi-functional platform for Cd2+ sensing and nitrocompound catalysis

Herein, through the interfacial regulation of cucurbiturils (CBs) on Fe₃O₄-Au nanoparticles, a novel multifunctional platform is constructed for the sensitive detection of Cd²⁺ and the selective catalytic reduction (SCR) of nitrocompounds. The reported surface modification strategy provides an efficient approach to prepare a new platform for multiple purposes.

Oligomeric Cucurbituril Complexes: from Peculiar Assemblies to Emerging Applications

Proteins are an endless source of inspiration. By carefully tuning the amino-acid sequence of proteins, nature made them evolve from primary to quaternary structures, a property specific to protein oligomers and often crucial to accomplish their function. On the other hand, the synthetic macrocycles cucurbiturils (CBs) have shown outstanding recognition properties in water, and a growing number of (host)_n :(guest)_n supramolecular polymers involving CBs have been reported. However, the burgeoning field of discrete (n:n) host:guest oligomers has just started to attract attention. While 2:2 complexes are the major oligomers, 3:3 and up to 6:6 oligomers have been described, some associated with emerging applications, specific to the (n:n) arrangements. Design rules to target (n:n) host:guest oligomers are proposed toward new advanced host:guest systems.

Complexation of biologically essential (mono- and divalent) metal cations to cucurbiturils: a DFT/SMD evaluation of the key factors governing the host-guest recognition

Supramolecular complexes based on classical synthetic macrocyclic host molecules such as cyclodextrins and calixarenes have received much attention recently due to their broad applications as biological and chemical sensors, bioimaging agents, drug delivery carriers, light-emitting materials, etc. Cucurbit[n]urils comprise another group of cavitands known for their high affinity for various guest molecules. Nonetheless, some aspects of their coordination chemistry remain enigmatic. Although they are recognized as potential biomimetic scaffolds, they are still not tested as metalloenzyme models and not much is known about their metal-binding properties. Furthermore, there is no systematic study on the key factors controlling the processes of metal coordination to these systems. In the computational study herein, DFT molecular modeling has been employed in order to investigate the interactions of biologically essential (mono- and divalent) metal cations to cucurbit[n]urils and evaluate the major determinants shaping the process. The thermodynamic descriptors (Gibbs energies in the gas phase and in a water medium) of the corresponding complexation reactions have been estimated. The results obtained shed light on the mechanism of host-guest recognition and disclose which factors more specifically affect the metal binding process.

Macrocyclic Arenes Functionalized with BODIPY: Rising Stars among Chemosensors and Smart Materials

Macrocycles play a crucial role in supramolecular chemistry and the family of macrocyclic arenes represents one of the most important types of hosts. Among them, calixarenes, resorcinarenes and pillararenes are the most commonly encountered macrocyclic arenes, and they have received considerable attention. Boron-dipyrromethene (BODIPY) dyes are fascinating compounds with multiple functionalization sites and outstanding luminescence properties including high fluorescence quantum yields, large molar absorption coefficients and remarkable photo- and chemical stability. The combination of macrocyclic arenes and BODIPY dyes has been demonstrated to be an effective strategy to construct chemosensors for various guests and smart materials with tailored properties. Herein, we firstly summarize the recent advances made so far in macrocyclic arenes substituted with BODIPY. This review only focuses on the three macrocyclic arenes of calixarenes, resorcinarenes and pillararenes, as there are no other macrocyclic arenes substituted BODIPY units at the present time. Hopefully, this review will not only afford a guide and useful information for those who are interested in developing novel chemosensors and smart materials, but also inspire new opportunities in this field.

Synthesis, Adsorption, and Recognition Properties of a Solid Symmetric Tetramethylcucurbit[6]uril-Based Porous Supramolecular Framework

In this work, we reported a porous supramolecular framework (A) constructed of a symmetric tetramethylcucurbit[6]uril (TMeQ[6]) in aqueous HCl solutions; the driving force was the outer surface interaction of cucurbit[n]urils, as well as hydrogen bonding between latticed water molecules and portal carbonyl oxygens of TMeQ[6]. Adsorption experimental results revealed that the porous supramolecular framework can absorb certain fluorophore guests (FGs) to form luminescent assemblies (FG@As) by fluorescence enhancement or colour change, and some of them can respond to certain volatile organic compounds. Thus, the TMeQ[6]-based supramolecular framework could be used as a sensor for certain gas or volatile compounds.