Fluorometric Recognition of Nucleotides within a Water-Soluble Tetrahedral Capsule

Unraveling the structure-chirality sensing relationship between achiral anthracene-based tetracationic nanotubes and nucleosides in aqueous host-guest complexation

In biological systems, nucleosides play crucial roles in various physiological processes. In this study, we designed and synthesized four achiral anthracene-based tetracationic nanotubes (1-4) as artificial hosts and chiroptical sensors for nucleosides in aqueous media. Notably, different nanotubes exhibit varied chirality sensing on circular dichroism (CD)/circularly polarized luminescence (CPL) spectra through the host-guest complexation, which prompted us to explore the factors influencing their chiroptical responses. Through systematic host-guest experiments, the structure-chirality sensing relationship between achiral anthracene-based tetracationic nanotubes and nucleosides in the host-guest complexation was unraveled. Firstly, the CD response originates from the anthracene rings situated at the side-wall position, resulting from the right-handed (P)- or left-handed (M)-twisted conformation of the macrocyclic structure. Secondly, the CPL signal is influenced by the presence of anthracene rings at the linking-wall position, which results from intermolecular chiral twisted stacking between these anthracene rings. Therefore, these nanotubes can serve as chiroptical sensor arrays to enhance the accuracy of nucleotide recognition through principal component analysis (PCA) analysis based on the diversified CD spectra. This study provides insights for the construction of adaptive chirality from achiral nanotubes with dynamic conformational nature and might facilitate further design of chiral functional materials for several applications.

Enzymatic Activation and Continuous Electrochemical Production of Methane from Dilute CO2 Sources with a Self-Healing Capsule

Converting dilute CO2 source into value-added chemicals and fuels is a promising route to reduce fossil fuel consumption and greenhouse gas emission, but integrating electrocatalysis with CO2 capture still faced marked challenges. Herein, we show that a self-healing metal-organic macrocycle functionalized as an electrochemical catalyst to selectively produce methane from flue gas and air with the lowest applied potential so far (0.06 V vs reversible hydrogen electrode, RHE) through an enzymatic activation fashion. The capsule emulates the enzyme' pocket to abstract one in situ-formed CO2-adduct molecule with the commercial amino alcohols, forming an easy-to-reduce substrate-involving clathrate to combine the CO2 capture with electroreduction for a thorough CO2 reduction. We find that the self-healing system exhibited enzymatic kinetics for the first time with the Michaelis-Menten mechanism in the electrochemical reduction of CO2 and maintained a methane Faraday efficiency (FE) of 74.24% with a selectivity of over 99% for continuous operation over 200 h. A consecutive working lab at 50 mA·cm-2, in an eleven-for-one (10 h working and 1 h healing) electrolysis manner, gives a methane turnover number (TON) of more than 10,000 within 100 h. The integrated electrolysis with CO2 capture facilitates the thorough reduction of flue gas (ca. 13.0% of CO2) and first time of air (ca. 400 ppm of CO2 to 42.7 mL CH4 from 1.0 m3 air). The new self-healing strategy of molecular electrocatalyst with an enzymatic activation manner and anodic shifting of the applied potentials provided a departure from the existing electrochemical catalytic techniques.

Proton-Induced Reversible Spin-State Switching in Octanuclear FeIII Spin-Crossover Metal-Organic Cages

Responsive spin-crossover (SCO) metal-organic cages (MOCs) are emerging dynamic platforms with potential for advanced applications in magnetic sensing and molecular switching. Among these, FeIII-based MOCs are particularly noteworthy for their air stability, yet they remain largely unexplored. Herein, we report the synthesis of two novel FeIII MOCs using a bis-bidentate ligand approach, which exhibit SCO activity above room temperature. These represent the first SCO-active FeIII cages and feature an atypical {FeN6}-type coordination sphere, uncommon for FeIII SCO compounds. Our study reveals that these MOCs are sensitive to acid/base variations, enabling reversible magnetic switching in solution. The presence of multiple active proton sites within these SCO-MOCs facilitates multisite, multilevel proton-induced spin-state modulation. This behavior is observed at room temperature through 1H NMR spectroscopy, capturing the subtle proton-induced spin-state transitions triggered by pH changes. Further insights from extended X-ray absorption fine structure (EXAFS) and theoretical analyses indicate that these magnetic alterations primarily result from the protonation and deprotonation processes at the NH active sites on the ligands. These processes induce changes in the secondary coordination sphere, thereby modulating the magnetic properties of the cages. The capability of these FeIII MOCs to integrate magnetic responses with environmental stimuli underscores their potential as finely tunable magnetic sensors and highlights their versatility as molecular switches. This work paves the way for the development of SCO-active materials with tailored properties for applications in sensing and molecular switching.

CageCavityCalc (C3): A Computational Tool for Calculating and Visualizing Cavities in Molecular Cages

Organic(porous) and metal-organic cages are promising biomimetic platforms with diverse applications spanning recognition, sensing, and catalysis. The key to the emergence of these functions is the presence of well-defined inner cavities capable of binding a wide range of guest molecules and modulating their properties. However, despite the myriad cage architectures currently available, the rational design of structurally diverse and functional cages with specific host-guest properties remains challenging. Efficiently predicting such properties is critical for accelerating the discovery of novel functional cages. Herein, we introduce CageCavityCalc (C3), a Python-based tool for calculating the cavity size of molecular cages. The code is available on GitHub at https://github.com/VicenteMartiCentelles/CageCavityCalc. C3 utilizes a novel algorithm that enables the rapid calculation of cavity sizes for a wide range of molecular structures and porous systems. Moreover, C3 facilitates easy visualization of the computed cavity size alongside hydrophobic and electrostatic potentials, providing insights into host-guest interactions within the cage. Furthermore, the calculated cavity can be visualized using widely available visualization software, such as PyMol, VMD, or ChimeraX. To enhance user accessibility, a PyMol plugin has been created, allowing nonspecialists to use this tool without requiring computer programming expertise. We anticipate that the deployment of this computational tool will significantly streamline cage cavity calculations, thereby accelerating the discovery of functional cages.

Biomimetic Hydrogen-Bonded G ⋅ C ⋅ G ⋅ C Quadruplex within a Tetraphenylethene-Based Octacationic Spirobicycle in Water

In biological systems, nucleotide quadruplexes (such as G-quadruplexes) in DNA and RNA that are held together by multiple hydrogen bonds play a crucial functional role. The biomimetic formation of these hydrogen-bonded quadruplexes captured by artificial systems in water poses a significant challenge but can offer valuable insights into these complex functional structures. Herein, we report the formation of biomimetic hydrogen-bonded G ⋅ C ⋅ G ⋅ C quadruplex captured by a tetraphenylethene (TPE) based octacationic spirobicycle (1). The spirobicyclic compound possesses a three-dimensional (3D) crossing dual-cavity structure, which enables the encapsulation of four d(GpC) dinucleotide molecules, thereby realizing 1 : 4 host-guest complexation in water. The X-ray structure reveals that four d(GpC) molecules further form a two-layer G ⋅ C ⋅ G ⋅ C quadruplex with Watson-Crick hydrogen bonds, which are stabilized within the dual hydrophobic cavities of 1 through the cooperative non-covalent interactions of hydrogen bonds, CH⋅⋅⋅π interactions, and hydrophobic effect. Due to the dynamically-rotational propeller chirality of TPE units, 1 with adaptive chirality can further serve as a chiroptical sensor to exhibit opposite Cotton effects with mirror-image CD spectra for the pH-dependent hydrogen-bonded assemblies of d(GpC) including the Watson-Crick G ⋅ C ⋅ G ⋅ C (pH 9.22) and Hoogsteen G ⋅ C+ ⋅ G ⋅ C+ (pH 5.74) quartets through the host-guest chirality transfer in water.

Metal-organic cages for gas adsorption and separation

The unique high surface area and tunable cavity size endow metal-organic cages (MOCs) with superior performance and broad application in gas adsorption and separation. Over the past three decades, for instance, numerous MOCs have been widely explored in adsorbing diverse types of gas including energy gases, greenhouse gases, toxic gases, noble gases, etc. To gain a better understanding of the structure-performance relationships, great endeavors have been devoted to ligand design, metal node regulation, active metal site construction, cavity size adjustment, and function-oriented ligand modification, thus opening up routes toward rationally designed MOCs with enhanced capabilities. Focusing on the unveiled structure-performance relationships of MOCs towards target gas molecules, this review consists of two parts, gas adsorption and gas separation, which are discussed separately. Each part discusses the cage assembly process, gas adsorption strategies, host-guest chemistry, and adsorption properties. Finally, we briefly overviewed the challenges and future directions in the rational development of MOC-based sorbents for application in challenging gas adsorption and separation, including the development of high adsorption capacity MOCs oriented by adsorbability and the development of highly selective adsorption MOCs oriented by separation performance.

Selective turn-on sensing of adenosine diphosphate and phosphate anions by ruthenium (II) polypyridine anchored p-tert-butylcalix[4]arene platform

BACKGROUND

Nucleoside polyphosphate (NPP) anions are important for enzymatic activity and should be monitored by scientists in industry and medicine. By elucidating enzyme kinetics and processes, it aids in the discovery of effective inhibitors and activators. Nucleoside polyphosphate (NPP) anions are used by kinases, GTPases, and glycosyltransferases (GTs). Phosphorylation of certain amino acid residues (Ser, Thr, and Tyr) on proteins requires the breakdown of ATP by protein kinases, which produces ADP. Protein kinases, breakdown of ATP, and NPP are the focus of oncology drug development because the aberrant control of kinase activity is a common cause of cancer.

RESULTS

However, a discriminative turn-on fluorescent property is exhibited by non-fluorescent p-tertbutylcalix[4]arene modified 1,2,3-triazole containing bis-ruthenium polypyridyl complex (RL) upon the addition of phosphate anions such as (dihydrogen pyrophosphate (H2P2O72-) and dihydrogen phosphate (H2PO4-)) in CH3CN solvent and Adenosine Diphosphate (ADP) in CH3CN/HEPES (pH = 7.4) buffer (9/1, v/v). The probe RL shows a better-recognizing ability with pyrophosphate anion (H2P2O72-) than dihydrogen phosphate anion (H2PO4-). With H2P2O72- and H2PO4- anions, the RL detection limit was calculated to be as low as 83 nM and 198 nM, respectively.

SIGNIFICANCE

The calix[4]arene macrocycle's excellent size and binding cone conformation make it a good host-guest interface for the pyrophosphate anion and ADP. The bis-ruthenium polypyridyl complex's connection to the p-tertbutyl calix[4]arene moiety creates the ADP selectivity turn-on sensor. When moving from mono-nuclear to bi-nuclear ruthenium complex anchored on p-tertbutyl calix[4]arene, the probe can differentiate ADP, ATP, and AMP. Furthermore, this platform is a great resource for creating devices to simultaneously assess phosphate anions in environmental samples.

Cage Match: Comparing the Anion Binding Ability of Isostructural Versus Isofunctional Pairs of Metal-Organic Nanocages

Affinities of six anions (mesylate, acetate, trifluoroacetate, p-toluenecarboxylate, p-toluenesulfonate, and perfluorooctanoate) for three related Pt2+ -linked porphyrin nanocages were measured to probe the influence of different noncovalent recognition motifs (e. g., hydrogen bonding, electrostatics, π bonding) on anion binding. Two new hosts of M6 L3 12+ (1b) and M4 L2 8+ (2) composition (M=(en)Pt2+ , L=(3-py)4 porphyrin) were prepared in a one-pot synthesis and allowed comparison of hosts that differ in structure while maintaining similar N-H hydrogen-bond donor ability. Comparisons of isostructural hosts that differ in hydrogen-bonding ability were made between 1b and a related M6 L3 12+ nanoprism (1a, M=(tmeda)Pt2+ ) that lacks N-H groups. Considerable variation in association constants (K1 =1.6×103  M-1 to 1.3×108  M-1 ) and binding mode (exo vs. endo) were found for different host-guest combinations. Strongest binding was seen between p-toluenecarboxylate and 1b, but surprisingly, association of this guest with 1a was only slightly weaker despite the absence of NH⋅⋅⋅O interactions. The high affinity between p-toluenecarboxylate and 1a could be turned off by protonation, and this behavior was used to toggle between the binding of this guest and the environmental pollutant perfluorooctanoate, which otherwise has a lower affinity for the host.

Allosterically Regulated Guest Binding Determines Framework Symmetry for an FeII 4 L4 Cage

Self-assembly of a flexible tritopic aniline and 3-substituted 2-formylpyridine subcomponents around iron(II) templates gave rise to a low-spin FeII 4 L4 capsule, whereas a high-spin FeII 3 L2 sandwich species formed when a sterically hindered 6-methyl-2-formylpyridine was used. The FeII 4 L4 cage adopted a new structure type with S4 symmetry, having two mer-Δ and two mer-Ʌ metal vertices, as confirmed by NMR and X-ray crystallographic analysis. The flexibility of the face-capping ligand endows the resulting FeII 4 L4 framework with conformational plasticity, enabling it to adapt structurally from S4 to T or C3 symmetry upon guest binding. The cage also displayed negative allosteric cooperativity in simultaneously binding different guests within its cavity and at the apertures between its faces.

Charge-Assisted Halogen Bonding in an Ionic Cavity of a Coordination Cage Based on a Copper(I) Iodide Cluster

The design of molecular containers capable of selectively binding specific guest molecules presents an interesting synthetic challenge in supramolecular chemistry. Here, we report the synthesis and structure of a coordination cage assembled from Cu₃ I₄ ^- clusters and tripodal cationic N-donor ligands. Owing to the localized permanent charges in the ligand core the cage binds iodide anions in specific regions within the cage through ionic interactions. This allows the selective binding of bromomethanes as secondary guest species within the cage promoted by halogen bonding, which was confirmed by single-crystal X-ray diffraction.

Metal Organic Polygons and Polyhedra: Instabilities and Remedies

The field of coordination chemistry has undergone rapid transformation from preparation of monometallic complexes to multimetallic complexes. So far numerous multimetallic coordination complexes have been synthesized. Multimetallic coordination complexes with well-defined architectures are often called as metal organic polygons and polyhedra (MOPs). In recent past, MOPs have received tremendous attention due to their potential applicability in various emerging fields. However, the field of coordination chemistry of MOPs often suffer set back due to the instability of coordination complexes particularly in aqueous environment-mostly by aqueous solvent and atmospheric moisture. Accordingly, the fate of the field does not rely only on the water solubilities of newly synthesized MOPs but very much dependent on their stabilities both in solution and solid state. The present review discusses several methodologies to prepare MOPs and investigates their stabilities under various circumstances. Considering the potential applicability of MOPs in sustainable way, several methodologies (remedies) to enhance the stabilities of MOPs are discussed here.

Pseudo-heterolepticity in Low-Symmetry Metal-Organic Cages

Heteroleptic metal-organic cages, formed through integrative self-assembly of ligand mixtures, are highly attractive as reduced symmetry supramolecular hosts. Ensuring high-fidelity, non-statistical self-assembly, however, presents a significant challenge in molecular engineering due to the inherent difficulty in predicting thermodynamic energy landscapes. In this work, two conceptual strategies are described that circumvent this issue, using ligand design strategies to access structurally sophisticated metal-organic hosts. Using these approaches, it was possible to realise cavity environments described by two inequivalent, unsymmetrical ligand frameworks, representing a significant step forward in the construction of highly anisotropic confined spaces.

Water-Soluble Self-Assembled Cage with Triangular Metal-Metal-Bonded Units Enabling the Sequential Selective Separation of Alkanes and Isomeric Molecules

The selective separation of structurally similar aliphatic/aromatic hydrocarbons is an essential goal in industrial processes. In this study, we report the synthesis of a water-soluble (Tr₂M₃)₄L₄ (Tr = cycloheptatrienyl ring; M = metal; L = organosulfur ligand) molecular cage (1) via self-assembly of the water-soluble acceptor tripalladium sandwich species [(Tr₂Pd₃)(CH₃CN)][NO₃]₂ and the attachment onto L of solubilizing methoxyethoxy appendants to be utilized in an energy-friendly alternative approach to the separation of structurally similar molecules under ambient conditions. Cage 1, comprising a hydrophobic inner cavity, exhibited good solubility and stability in aqueous media. It also demonstrated excellent performance in the sequential separation of alkanes (C6-C9), xylene, and other disubstituted benzene isomers and cis/trans-decalin.

A Fluorescent Cage for Supramolecular Sensing of 3‐Nitrotyrosine in Human Blood Serum

3‐Nitrotyrosine (NT) is generated by the action of peroxynitrite and other reactive nitrogen species (RNS), and as a consequence it is accumulated in inflammation‐associated conditions. This is particularly relevant in kidney disease, where NT concentration in blood is considerably high. Therefore, NT is a crucial biomarker of renal damage, although it has been underestimated in clinical diagnosis due to the lack of an appropriate sensing method. Herein we report the first fluorescent supramolecular sensor for such a relevant compound: Fluorescence by rotational restriction of tetraphenylethenes (TPE) in a covalent cage is selectively quenched in human blood serum by 3‐nitrotyrosine (NT) that binds to the cage with high affinity, allowing a limit of detection within the reported physiological concentrations of NT in chronic kidney disease.

Transformation networks of metal-organic cages controlled by chemical stimuli

The flexibility of biomolecules enables them to adapt and transform as a result of signals received from the external environment, expressing different functions in different contexts. In similar fashion, coordination cages can undergo stimuli-triggered transformations owing to the dynamic nature of the metal-ligand bonds that hold them together. Different types of stimuli can trigger dynamic reconfiguration of these metal-organic assemblies, to switch on or off desired functionalities. Such adaptable systems are of interest for applications in switchable catalysis, selective molecular recognition or as transformable materials. This review highlights recent advances in the transformation of cages using chemical stimuli, providing a catalogue of reported strategies to transform cages and thus allow the creation of new architectures. Firstly we focus on strategies for transformation through the introduction of new cage components, which trigger reconstitution of the initial set of components. Secondly we summarize conversions triggered by external stimuli such as guests, concentration, solvent or pH, highlighting the adaptation processes that coordination cages can undergo. Finally, systems capable of responding to multiple stimuli are described. Such systems constitute composite chemical networks with the potential for more complex behaviour. We aim to offer new perspectives on how to design transformation networks, in order to shed light on signal-driven transformation processes that lead to the preparation of new functional metal-organic architectures.

Computational Modeling of Supramolecular Metallo-organic Cages-Challenges and Opportunities

Self-assembled metallo-organic cages have emerged as promising biomimetic platforms that can encapsulate whole substrates akin to an enzyme active site. Extensive experimental work has enabled access to a variety of structures, with a few notable examples showing catalytic behavior. However, computational investigations of metallo-organic cages are scarce, not least due to the challenges associated with their modeling and the lack of accurate and efficient protocols to evaluate these systems. In this review, we discuss key molecular principles governing the design of functional metallo-organic cages, from the assembly of building blocks through binding and catalysis. For each of these processes, computational protocols will be reviewed, considering their inherent strengths and weaknesses. We will demonstrate that while each approach may have its own specific pitfalls, they can be a powerful tool for rationalizing experimental observables and to guide synthetic efforts. To illustrate this point, we present several examples where modeling has helped to elucidate fundamental principles behind molecular recognition and reactivity. We highlight the importance of combining computational and experimental efforts to speed up supramolecular catalyst design while reducing time and resources.

Metal-organic cages against toxic chemicals and pollutants

The continuous release of toxic chemicals and pollutants into the atmosphere and natural waters threatens, directly and indirectly, human health, the sustainability of the planet, and the future of society. Materials capable of capturing or chemically inactivating hazardous substances, which are harmful to humans and the environment, are critical in the modern age. Metal-organic cages (MOCs) show great promise as materials against harmful agents both in solution and in solid state. This Highlight features examples of MOCs that selectively encapsulate, adsorb, or remove from a medium noxious gases, toxic organophosphorus compounds, water pollutant oxoanions, and some emerging organic contaminants. Remarkably, the toxicity of interacting contaminants may be lowered by MOCs as well. Specific cases pertaining to the use of these cages for the chemical degradation of some harmful substances are presented. This Highlight thus aims to provide an overview of the possibilities of MOCs in this area and new methodological insights into their operation for enhancing their activity and the engineering of further remediation applications.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Templation and Concentration Drive Conversion Between a FeII12L12 Pseudoicosahedron, a FeII4L4 Tetrahedron, and a FeII2L3 Helicate

We report the construction of three structurally distinct self-assembled architectures: Fe^II₁₂L₁₂ pseudoicosahedron 1, Fe^II₂L₃ helicate 2, and Fe^II₄L₄ tetrahedron 3, formed from a single triazatriangulenium subcomponent A under different reaction conditions. Pseudoicosahedral capsule 1 is the largest formed through subcomponent self-assembly to date, with an outer-sphere diameter of 5.4 nm and a cavity volume of 15 nm³. The outcome of self-assembly depended upon concentration, where the formation of pseudoicosahedron 1 was favored at higher concentrations, while helicate 2 exclusively formed at lower concentrations. The conversion of pseudoicosahedron 1 or helicate 2 into tetrahedron 3 occurred following the addition of a CB₁₁H₁₂^- or B₁₂F₁₂^2- template.

Straight from the bottle! Wine and juice dicarboxylic acids as templates for supramolecular cage self-assembly

Two imine based supramolecular cages are able to self-assemble in the presence of a complex mixture like wine or fruit juices. Taking advantage of templating agents present in these mixtures the systems are able to form and to selectively encapsulate dicarboxylic systems present in the mixtures. This capability has been exploited to develop molecular systems able to report the enantiomeric excess and composition of (a)chiral dicarboxylic acids in fruit juices and wines using ¹H-NMR.

Tuning the physicochemical properties of reticular covalent organic frameworks (COFs) for biomedical applications

Since the first report by Yaghi's group in 2005, research enthusiasm has been increasingly raised to synthesize diverse crystalline porous materials as -B-O-, -C-N-, -C-C-, and -C-O- linkage-based COFs. Recently, the biomedical applications of COFs have become more and more attractive in biomedical applications, including drug delivery, bioimaging, biosensing, antimicrobial, and therapeutic applications, as these materials bear well-defined crystalline porous structures and well-customized functionalities. However, the clinical translation of these research findings is challenging due to the formidable hindrances for in vivo use, such as low biocompatibility, poor selectivity, and long bio-persistence. Some attempts have raised a promising solution towards these obstacles by tailored engineering the functionalities of COFs. To speed up the clinical translations of COFs, a short review of principles and strategies to tune the physicochemical properties of COFs is timely and necessary. In this review, we summarized the biomedical utilities of COFs and discussed the related key physicochemical properties. To improve the performances of COFs in biomedical uses, we propose approaches for the tailored functionalization of COFs, including large-scale manufacture, standardization in nanomedicines, enhancing targeting efficacy, maintaining predesigned functions upon transformations, and manipulation of multifunctional COFs. We expect that this minireview strengthens the fundamental understandings of property-bioactivity relationships of COFs and provides insights for the rational design of their high-order reticular structures.

Hierarchical Two-Level Supramolecular Chirality of an Achiral Anthracene-Based Tetracationic Nanotube in Water

Herein, we report an achiral anthracene-based tetracationic nanotube (1⋅4Cl^- ) that shows two levels of supramolecular chirality: namely, conformationally adaptive host-guest complexation with nucleoside triphosphates (e.g. ATP, GTP, CTP, and UTP) and twisted packing of the chiral host-guest complexes in water. Interestingly, achiral 1⋅4Cl^- exhibits chiral recognition for ATP/GTP and CTP/UTP through structural transformation of its intramolecular M- and P-twisted conformation as the first level of supramolecular chirality, which leads to adaptive chirality with opposite CD responses. Furthermore, the formation of chiral M-1⋅4Cl^- ⊃ATP can promote an intermolecular P-twisted dimeric packing of anthracene rings as the second level of supramolecular chirality to achieve assembled chirality with strong circularly polarized luminescence arising from the excimer ((+)-CPL, g_lum ≈10^-2 ) in water.

Supramolecular Coordination Complexes as Optical Biosensors

In recent years, luminescent supramolecular coordination complexes (SCCs), including 2D-metallacycles and 3D-metallacages have been utilised for biomolecular analysis. Unlike small-molecular probes, the dimensions, size, shape, and flexibility of these complexes can easily be tuned by combining ligands designed with particular geometries, symmetries and denticity with metal ions with strong geometrical binding preferences. The well-defined cavities that result, in combination with the other non-covalent interactions that can be programmed into the ligand design, facilitate great selectivity towards guest binding. In this Review we will discuss the application of luminescent metallacycles and cages in the binding and detection of a wide range of biomolecules, such as carbohydrates, proteins, amino acids, and biogenic amines. We aim to explore the effect of the structural diversity of SCCs on the extent of biomolecular sensing, expressed in terms of sensitivity, selectivity and detection range.

Mimicking Biological Recognition: Lessons in Binding Hydrophilic Guests in Water

Selective molecular recognition of hydrophilic guests in water plays a fundamental role in a vast number of biological processes, but synthetic mimicry of biomolecular recognition in water still proves challenging both in terms of achieving comparable affinities and selectivities. This Review highlights strategies that have been developed in the field of supramolecular chemistry to selectively and non-covalently bind three classes of biologically relevant molecules: nucleotides, carbohydrates, and amino acids. As several groups have systematically modified receptors for a specific guest, an evolutionary perspective is also provided in some cases. Trends in the most effective binding forces for each class are described, providing insight into selectivity and potential directions for future work.

Supramolecular Fluorescent Sensors: An Historical Overview and Update

Since as early as 1867, molecular sensors have been recognized as being intelligent "devices" capable of addressing a variety of issues related to our environment and health (e.g., the detection of toxic pollutants or disease-related biomarkers). In this review, we focus on fluorescence-based sensors that incorporate supramolecular chemistry to achieve a desired sensing outcome. The goal is to provide an illustrative overview, rather than a comprehensive listing of all that has been done in the field. We will thus summarize early work devoted to the development of supramolecular fluorescent sensors and provide an update on recent advances in the area (mostly from 2018 onward). A particular emphasis will be placed on design strategies that may be exploited for analyte sensing and corresponding molecular platforms. Supramolecular approaches considered include, inter alia, binding-based sensing (BBS) and indicator displacement assays (IDAs). Because it has traditionally received less treatment, many of the illustrative examples chosen will involve anion sensing. Finally, this review will also include our perspectives on the future directions of the field.

Design and Applications of Water-Soluble Coordination Cages

Compartmentalization of the aqueous space within a cell is necessary for life. In similar fashion to the nanometer-scale compartments in living systems, synthetic water-soluble coordination cages (WSCCs) can isolate guest molecules and host chemical transformations. Such cages thus show promise in biological, medical, environmental, and industrial domains. This review highlights examples of three-dimensional synthetic WSCCs, offering perspectives so as to enhance their design and applications. Strategies are presented that address key challenges for the preparation of coordination cages that are soluble and stable in water. The peculiarities of guest binding in aqueous media are examined, highlighting amplified binding in water, changing guest properties, and the recognition of specific molecular targets. The properties of WSCC hosts associated with biomedical applications, and their use as vessels to carry out chemical reactions in water, are also presented. These examples sketch a blueprint for the preparation of new metal-organic containers for use in aqueous solution, as well as guidelines for the engineering of new applications in water.

Oxidation triggers guest dissociation during reorganization of an FeII 4L6 twisted parallelogram

A three-dimensional FeII 4L6 parallelogram was prepared from ferrocene-containing ditopic ligands. The steric preference of the bulky ferrocene cores towards meridional vertex coordination brought about this new structure type, in which the ferrocene units adopt three distinct conformations. The structure possesses two distinct, bowl-like cavities that host anionic guests. Oxidation of the ferrocene FeII to ferrocenium FeIII causes rotation of the ferrocene hinges, converting the structure to an FeII 1L1 + species with release of anionic guests, even though the average charge per iron increases in a way that would ordinarily increase guest binding strength. The degrees of freedom exhibited by these new structures - derived from the different configurations of the three ligands surrounding a meridional FeII center and the rotation of ferrocene cores - thus underpin their ability to reconfigure and eject guests upon oxidation.

Coordinative-to-covalent transformation, isomerization dynamics, and logic gate application of dithienylethene based photochromic cages

Photochromic coordinative cages containing dynamic C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N imine bonds are assembled from a dithienylethene-based aldehyde and tris-amine precursors via metallo-component self-assembly. The resulting metal-templated cages are then reduced and demetalated into pure covalent-organic cages (COCs), which are otherwise difficult to prepare via de novo organic synthesis. Both the obtained coordinative and covalent cages can be readily interconverted between the ring-open (o-isomer) and one-lateral ring-closed (c-isomer) forms by UV/vis light irradiation, demonstrating distinct absorption, luminescence and photoisomerization dynamics. Specifically, the ring-closed c-COCs show a blue-shifted absorption band compared with analogous metal-templated cages, which can be applied in photoluminescence (PL) color-tuning of upconversion materials in different ways, showing potential for constructing multi-readout logic gate systems.

Metal-templated component self-assembly and then demetalation affords photochromic covalent organic cages applicable for upconversion PL-color tuning for logic gates.

Chemosensing of Guanosine Triphosphate Based on a Fluorescent Dinuclear Zn(II)-Dipicolylamine Complex in Water

Guanosine triphosphate (GTP) is a key biomarker of multiple cellular processes and human diseases. The new fluorescent dinuclear complex [Zn₂(L)(S)][OTf]₄, 1 (asymmetric ligand, L = 5,8-Bis{[bis(2-pyridylmethyl)amino] methyl}quinoline, S = solvent, and OTf = triflate anion) was synthesized and studied in-depth as a chemosensor for nucleoside polyphosphates and inorganic anions in pure water. Additions at neutral pH of nucleoside triphosphates, guanosine diphosphate, guanosine monophosphate, and pyrophosphate (PPi) to 1 quench its blue emission (λ_em = 410 nm) with a pronounced selectivity toward GTP over other anions, including adenosine triphosphate (ATP), uridine triphosphate (UTP), and cytidine triphosphate (CTP). The efficient quenching response by the addition of GTP was observed in the presence of coexisting species in blood plasma and urine with a detection limit of 9.2 μmol L^-1. GTP also shows much tighter binding to the receptor 1 on a submicromolar level. On the basis of multiple spectroscopic tools (¹H, ³¹P NMR, UV-vis, and fluorescence) and DFT calculations, the binding mode is proposed through three-point recognition involving the simultaneous coordination of the N⁷ atom of the guanosine motif and two phosphate groups to the two Zn(II) atoms. Spectroscopic studies, MS-ESI, and DFT suggested that GTP bound to 1 in 1:1 and 2:2 models with high overall binding constants of log β_1 (1:1) = 6.05 ± 0.01 and log β₂ = 10.91 ± 0.03, respectively. The optical change and selectivity are attributed to the efficient binding of GTP to 1 by the combination of a strong electrostatic contribution and synergic effects of coordination bonds. Such GTP selectivity of an asymmetric metal-based receptor in water is still rare.

Eu(III) Tetrahedron Cage as a Luminescent Chemosensor for Rapidly Reversible and Turn-On Detection of Volatile Amine/NH3

Because of the involvement of the gas-solid diffusion, device fabrication, and the relatively complex photophysical process, the lanthanide complexes are rarely exploited as fluorescence sensors for volatile compound (VC) detection. Herein, we report the first example of a discrete 3D Ln-based architecture as a sensor for VCs. The designed Eu₄L₄ tetrahedral cage shows highly selective, rapidly reversible, and turn-on emissive responses toward volatile amines/NH₃ in a spin-coated film. Through the comprehensive spectral characteristic and density functional theory calculation, an intermolecular weak nucleophilic interaction is proposed for this response mechanism. Combining this weak interactions with the permeability of the cage, the film presents subsecond to second timescales rapid response; combining the fitting electrophilic capability of the β-diketonate units to amine nitrogen with the tunable intramolecular charge-transfer feature, the cage shows excellent selectivity and turn-on emissive response. This work provides a new clue to develop the lanthanide complexes as luminescence probes for VCs.

Electron transfer in the confined environments of metal–organic coordination supramolecular systems

In this review, we overview regulatory factors and diverse applications of electron transfer in confined environments of supramolecular host–guest systems.