G-quadruplex organic frameworks

Supramolecular Entanglement in a Hydrogen-Bonded Organic Framework Enables Flexible-Robust Porosity for Highly Efficient Purification of Natural Gas

The development of porous materials with flexible-robust characteristics shows some unique advantages to target high performance for gas separation, but remains a daunting challenge to achieve so far. Herein, we report a carboxyl-based hydrogen-bonded organic framework (ZJU-HOF-8a) with flexible-robust porosity for efficient purification of natural gas. ZJU-HOF-8a features a four-fold interpenetrated structure with dia topology, wherein abundant supramolecular entanglements are formed between the adjacent subnetworks through weak intermolecular hydrogen bonds. This structural configuration could not only stabilize the whole framework to establish the permanent porosity, but also enable the framework to show some flexibility due to its weak intermolecular interactions (so-called flexible-robust framework). The flexible-robust porosity of ZJU-HOF-8a was exclusively confirmed by gas sorption isotherms and single-crystal X-ray diffraction studies, showing that the flexible pore pockets can be opened by C3H8 and n-C4H10 molecules rather by C2H6 and CH4. This leads to notably higher C3H8 and n-C4H10 uptakes with enhanced selectivities than C2H6 over CH4 under ambient conditions, affording one of the highest n-C4H10/CH4 selectivities. The gas-loaded single-crystal structures coupled with theoretical simulations reveal that the loading of n-C4H10 can induce an obvious framework expansion along with pore pocket opening to improve n-C4H10 uptake and selectivity, while not for C2H6 adsorption. This work suggests an effective strategy of designing flexible-robust HOFs for improving gas separation properties.

Structural Design and Energy and Environmental Applications of Hydrogen-Bonded Organic Frameworks: A Systematic Review

Hydrogen-bonded organic frameworks (HOFs) are emerging porous materials that show high structural flexibility, mild synthetic conditions, good solution processability, easy healing and regeneration, and good recyclability. Although these properties give them many potential multifunctional applications, their frameworks are unstable due to the presence of only weak and reversible hydrogen bonds. In this work, the development history and synthesis methods of HOFs are reviewed, and categorize their structural design concepts and strategies to improve their stability. More importantly, due to the significant potential of the latest HOF-related research for addressing energy and environmental issues, this work discusses the latest advances in the methods of energy storage and conversion, energy substance generation and isolation, environmental detection and isolation, degradation and transformation, and biological applications. Furthermore, a discussion of the coupling orientation of HOF in the cross-cutting fields of energy and environment is presented for the first time. Finally, current challenges, opportunities, and strategies for the development of HOFs to advance their energy and environmental applications are discussed.

Intelligently optimized global analysis of time resolved spectra with particle swarm optimization

Time-resolved spectroscopy, especially transient absorption spectroscopy (TAS), provides valuable insights to excited state dynamics. Analyzing TAS data involves fitting complex kinetic traces at various probe wavelengths using different rate equations. Conventional TAS global fitting methods require domain experts to establish physically valid models and provide good initial guesses to generate converged solutions. This poses challenges for non-experts who seek to utilize TAS, thus limiting its broader application and impact. To address this problem, we propose an intelligent optimization framework based on the particle swarm optimization (PSO) algorithm. In the proposed method, the PSO algorithm acts as the global fitting method to find the optimal values of the target variables or unknown parameters in the kinetics models. The target solution is optimized by iteratively updating candidate solutions with respect to an objective feedback signal. We demonstrated the effectiveness of the proposed PSO-based global fitting method with both synthetic and experimental datasets. The results show that our proposed method can successfully find the optimal target values in the global fitting process automatically, thus eliminating the iterative manual labor traditionally required. The proposed intelligent optimization framework provides a novel approach for automatic global fitting of TAS data, which significantly enhances the accessibility and utilization of the TAS methodology.

Polymorphism of G-quadruplexes formed by short oligonucleotides containing a 3'-3' inversion of polarity: From G:C:G:C tetrads to π-π stacked G-wires

G-wires are supramolecular DNA structures based on the G-quadruplex (G4) structural motif obtained by the self-assembly of interlocked slipped G-rich oligonucleotide (ON) strands, or by end-to-end stacking of G4 units. Despite the increasing interest towards G-wires due to their potential applications in DNA nanotechnologies, the self-assembly process to obtain G-wires having a predefined length and stability is still neither completely understood nor controlled. In our previous studies, we demonstrated that the d(5'CG2-3'-3'-G2C5') ON, characterized by the presence of a 3'-3'-inversion of polarity site self-assembles into a G-wire structure when annealed in the presence of K+ ions. Herein, by using CD, PAGE, HPLC size exclusion chromatography, and NMR investigations we studied the propensity of shorter analogues having sequences 5'CGn-3'-3'-GmC5' (with n = 1 and 1 ≤ m ≤ 3) to form the corresponding G-quadruplexes and stacked G-wires. The results revealed that the formation of G-wires starting from d(5'CGn-3'-3'-GmC5') ONs is possible only for the sequences having n and m > 1 in which both guanosines flanking the 5'-ending cytosines are not involved into the 3'-3' phosphodiester bond.

Macrocycle Self-Assembly Hydrogel for High-Efficient Oil-Water Separation

Supramolecular hydrogels involved macrocycles have been explored widely in recent years, but it remains challenging to develop hydrogel based on solitary macrocycle with super gelation capability. Here, the construction of lantern[33 ]arene-based hydrogel with low critical gelation concentration (0.05 wt%), which can be used for efficient oil-water separation, is reported. The lantern[33 ]arenes self-assemble into hydrogen-bonded organic nanoribbons, which intertwine into entangled fibers to form hydrogel. This hydrogel which exhibits reversible pH-responsiveness characteristics can be coated on stainless-steel mesh by in situ sol-gel transformation. The resultant mesh exhibits excellent oil-water separation efficiency (>99%) and flux (>6 × 104 L m-2 h-1 ). This lantern[33 ]arene-based hydrogel not only sheds additional light on the gelation mechanisms for supramolecular hydrogels, but also extends the application of macrocycle-based hydrogels as functional interfacial materials.

Flexible Luminescent Hydrogen-bonded Organic Framework for the Separation of Benzene and Cyclohexane

A nonplanar phenothiazine derivative with three cyano moieties (PTTCN) is designed and synthesized to achieve functional crystals for absorptive separation of benzene and cyclohexane. PTTCN can crystallize into two kinds of crystals with different fluorescence colors in different solvent systems. The molecules in two crystals are in different stereo isomeric forms of nitrogen, quasi axial (ax), and quasi equatorial (eq). The crystals with blue fluorescence in ax form may selectively adsorb benzene by a single-crystal-to-single-crystal (SCSC) transformation, but separated benzene from a benzene/cyclohexane equimolar mixture with a low purity of 79.6%. Interestingly, PTTCN molecules with eq form and benzene co-assembled to construct a hydrogen-bonded framework (X-HOF-4) with S-type solvent channels and yellow-green fluorescence, and can release benzene to form nonporous guest-free crystal under heating. Such nonporous crystals strongly favor aromatic benzene over cyclohexane and may selectively reabsorb benzene from benzene/cyclohexane equimolar mixture to recover original framework, and the purity of benzene can reach ≈96.5% after release from framework. Moreover, reversible transformation between the nonporous crystals and the guest-containing crystals allows the material to be reused.

Nanoporous Crystalline Materials for the Recognition and Applications of Nucleic Acids

Nucleic acid plays a crucial role in countless biological processes. Hence, there is great interest in its detection and analysis in various fields from chemistry, biology, to medicine. Nanoporous crystalline materials exhibit enormous potential as an effective platform for nucleic acid recognition and application. These materials have highly ordered and uniform pore structures, as well as adjustable surface chemistry and pore size, making them good carriers for nucleic acid extraction, detection, and delivery. In this review, the latest developments in nanoporous crystalline materials, including metal organic frameworks (MOFs), covalent organic frameworks (COFs), and supramolecular organic frameworks (SOFs) for nucleic acid recognition and applications are discussed. Different strategies for functionalizing these materials are explored to specifically identify nucleic acid targets. Their applications in selective separation and detection of nucleic acids are highlighted. They can also be used as DNA/RNA sensors, gene delivery agents, host DNAzymes, and in DNA-based computing. Other applications include catalysis, data storage, and biomimetics. The development of novel nanoporous crystalline materials with enhanced biocompatibility has opened up new avenues in the fields of nucleic acid analysis and therapy, paving the way for the development of sensitive, selective, and cost-effective diagnostic and therapeutic tools with widespread applications.

Chalcogen-bridged coordination polymer for the photocatalytic activation of aryl halides

The ability to deliver electrons is vital for dye-based photocatalysts. Conventionally, the aromatic stacking-based charge-transfer complex increases photogenerated electron accessibility but decreases the energy of excited-state dyes. To circumvent this dilemma, here we show a strategy by tuning the stacking mode of dyes. By decorating naphthalene diimide with S-bearing branches, the S···S contact-linked naphthalene diimide string is created in coordination polymer, thereby enhancing electron mobility while simultaneously preserving competent excited-state reducing power. This benefit, along with in situ assembly between naphthalene diimide strings and exogenous reagent/reactant, improves the accessibility of short-lived excited states during consecutive photon excitation, resulting in greater efficiency in photoinduced electron-transfer activation of inert bonds in comparison to other coordination polymers with different dye-stacking modes. This heterogeneous approach is successfully applied in the photoreduction of inert aryl halides and the successive formation of C_Ar-C/S/P/B bonds with potential pharmaceutical applications.

Hybrid Hydrogen-Bonded Organic Frameworks: Structures and Functional Applications

As a new class of porous crystalline materials, hydrogen-bonded organic frameworks (HOFs) assembled from building blocks by hydrogen bonds have gained increasing attention. HOFs benefit from advantages including mild synthesis, easy purification, and good recyclability. However, some HOFs transform into unstable frameworks after desolvation, which hinders their further applications. Nowadays, the main challenges of developing HOFs lie in stability improvement, porosity establishment, and functionalization. Recently, more and more stable and permanently porous HOFs have been reported. Of all these design strategies, stronger charge-assisted hydrogen bonds and coordination bonds have been proven to be effective for developing stable, porous, and functional solids called hybrid HOFs, including ionic and metallized HOFs. This Review discusses the rational design synthesis principles of hybrid HOFs and their cutting-edge applications in selective inclusion, proton conduction, gas separation, catalysis and so forth.

Ion slippage through Li+-centered G-quadruplex

Single-ion conductors have garnered attention in energy storage systems as a promising alternative to currently widespread electrolytes that allow migration of cations and anions. However, ion transport phenomena of most single-ion conductors are affected by strong ion (e.g., Li⁺)-ion (immobilized anionic domains) interactions and tortuous paths, which pose an obstacle to achieving performance breakthroughs. Here, we present a Li⁺-centered G-quadruplex (LiGQ) as a class of single-ion conductor based on directional Li⁺ slippage at the microscopic level. A guanine derivative with liquid crystalline moieties is self-assembled to form a hexagonal ordered columnar structure in the LiGQ, thereby yielding one-dimensional central channels that provide weak ion-dipole interaction and straightforward ionic pathways. The LiGQ exhibits weak Li⁺ binding energy and low activation energy for ion conduction, verifying its viability as a new electrolyte design.

NIR-light-controlled G-quadruplex hydrogel for synergistically enhancing photodynamic therapy via sustained delivery of metformin and catalase-like activity in breast cancer

Severely hypoxic condition of tumour represents a notable obstacle against the efficiency of photodynamic therapy (PDT). While mitochondria targeted therapy by metformin has been considered as a promising strategy for reducing oxygen consumption in tumours, its low treatment sensitivity, short half-life and narrow absorption window in vivo remain the intractable challenges. In this report, 5′-guanosine monophosphate (5′GMP), indocyanine green (ICG), hemin and metformin, were combined to construct a smart G-quadruplex (G4) hydrogel named HMI@GEL for breast cancer (BC) treatment. Benefiting from the photothermal (PTT) effect of ICG, HMI@GEL exhibited excellent characteristics of NIR-light-triggered and persistent drug delivery to maintain high intratumoral concentration of metformin. Furthermore, drug loading concentration of metformin reached an amazing 300 ​mg ​mL⁻¹ in HMI@GEL. To our knowledge, it might be the highest loading efficiency in the reported literatures. With the combination of catalase-mimicking Hemin@mil88, metformin could inhibit tumour mitochondrial respiratory significantly, which sequentially permitted in situ efficient oxygen generation. Remarkable apoptosis and necrosis were achieved by the combination of PTT and synergistically enhanced PDT as well as the activated tumour immunotherapy. Collectively, the HMI@GEL in situ injectable platform showed a promising strategy for enhanced PDT by metformin, and opened new perspectives for treating BC versatilely.

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A NIR-light-controlled G-quadruplex hydrogel HMI@GEL loading metformin was prepared for precision breast cancer therapy.

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The extremely high drug loading capacity (300 ​mg ​mL⁻¹) and persistent delivery of metformin was realized for the first time.

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The combination of catalase-mimicking Hemin@mil88 and metformin dual enhanced intracellular ROS generation.

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The tumour immune microenvironment was dramatically reshaped by synthetic photodynamic/photothermal therapy.

Design Rules of Hydrogen-Bonded Organic Frameworks with High Chemical and Thermal Stabilities

Hydrogen-bonded organic frameworks (HOFs), self-assembled from strategically pre-designed molecular tectons with complementary hydrogen-bonding patterns, are rapidly evolving into a novel and important class of porous materials. In addition to their common features shared with other functionalized porous materials constructed from modular building blocks, the intrinsically flexible and reversible H-bonding connections endow HOFs with straightforward purification procedures, high crystallinity, solution processability, and recyclability. These unique advantages of HOFs have attracted considerable attention across a broad range of fields, including gas adsorption and separation, catalysis, chemical sensing, and electrical and optical materials. However, the relatively weak H-bonding interactions within HOFs can potentially limit their stability and potential use in further applications. To that end, this Perspective highlights recent advances in the development of chemically and thermally robust HOF materials and systematically discusses relevant design rules and synthesis strategies to access highly stable HOFs.

Guanine-Based G-Quadruplexes Templated by Various Cations toward Potential Use as Single-Ion Conductors

Inspired by the atomic-sized, shape-regulated features of G-quadruplexes comprising guanine motifs with a monovalent metal cation, the G-quadruplex-forming ability, and properties of a guanine-based π-conjugated Y2 molecule containing bithiophene and peripheral dodecyl chain units in the presence of various cation salts (Li⁺ , Na⁺ , K⁺ , and Mg²⁺ ) were exploited. A series of structural characterization revealed that Y2 yielded desirable G-quadruplexes with all the tested cations as a consequence of the combination of a hydrogen-bonded cyclic G-quartet, π-stacking, and cation-dipole interactions. The radius and nature of the coordinating cations crucially affected the structural characteristics of G-quadruplexes, leading to variations in the ion migration ability inside the cavity of the G-quadruplex (Li⁺ >Na⁺ >K⁺ >Mg²⁺ ), as characterized through theoretical and experimental investigations. These results not only improve the understanding of G-quadruplex self-assemblies based on guanine but also provide an impetus for their diverse potential applications, especially in the field of Li batteries.

Alkaline earth cations binding mode tailors excited-state charge transfer properties of guanine quadruplex: A TDDFT study

Quadruplexes formed by nucleic acids and their derivates tend to chelate different monovalent and bivalent cations, which simultaneously affect their excited electronic states properties. Cation binding to every and every other cavity of the central ion channel could be exploited for tuning exited-state charge transfer properties. In this work we utilize set of descriptors constructed on the basis of the one-electron transition density matrix obtained using linear-response TDDFT to study excited states properties of four crystallized tetramolecular quadruplexes that chelate alkaline earth cations (Ca²⁺, Sr²⁺ and Ba²⁺). Here, we show that alkaline earth cations situated at adjacent vacancies promote existence of the nucleobase-metal charge separation (CS) states, contrary to the structures with cations that occupy every second available vacancy. We argued that stabilization of these CS states is due to the strong electric field that stabilizes d orbitals of the cations which accept an excited-electron. Moreover, CS content is increased and redshifted below the first bright transition when number of the chelated cations is increased. Hydration effects stabilized CS states and increased their relative content. We also identified electron detachment states in the broad energy range for the Ca²⁺ containing system. These findings are valuable for understanding and development of the novel nanostructures based on the quadruplex scaffold with adjustable optical properties.

Heterocycle-modified 2'-Deoxyguanosine Nucleolipid Analogs Stabilize Guanosine Gels and Self-assemble to Form Green Fluorescent Gels

Nucleoside-lipid conjugates are very useful supramolecular building blocks to construct self-assembled architectures suited for biomedical and material applications. Such nucleoside derivatives can be further synthetically manipulated to endow additional functionalities that could augment the assembling process and impart interesting properties. Here, we report the design, synthesis and self-assembling process of multifunctional supramolecular nucleolipid synthons containing an environment-sensitive fluorescent guanine. The amphiphilic synthons are composed of an 8-(2-(benzofuran-2-yl)vinyl)-guanine core and alkyl chains attached to 3'-O and 5'-O-positions of 2'-deoxyguanosine. The 2-(benzofuran-2-yl)vinyl (BFV) moiety attached at the C8 position of the nucleobase adopted a syn conformation about the glycosidic bond, which facilitated the self-assembly process through the formation of a G-tetrad as the basic unit. While 3',5'-diacylated BFV-modified dG analog stabilized the guanosine hydrogel by hampering the crystallization process and imparted fluorescence, BFV-modified dGs containing longer alkyl chains formed a green fluorescent organogel, which transformed into a yellow fluorescent gel in the presence of a complementary non-fluorescent cytidine nucleolipid. The ability of the dG analog containing short alkyl chains to modulate the mechanical property of a gel, and interesting fluorescence properties and self-assembling behavior exhibited by the dG analogs containing long alkyl chains in response to heat and complementary base underscore the potential use of these new supramolecular synthons in material applications.

Electronic Level Structure of Novel Guanine Octuplex DNA Single Molecules

Throughout the past few decades, guanine quadruplex DNA structures have attracted much interest both from a fundamental material science perspective and from a technologically oriented perspective. Novel guanine octuplex DNA, formed from coiled quadruplex DNA, was recently discovered as a stable and rigid DNA-based nanostructure. A detailed electronic structure study of this new nanomaterial, performed by scanning tunneling spectroscopy on a subsingle-molecule level at cryogenic temperature, is presented herein. The electronic levels and lower energy gap of guanine octuplex DNA compared to quadruplex DNA dictate higher transverse conductivity through guanine octads than through guanine tetrads.

Self-assembly of rylene-decorated guanine ribbons on graphene surface for optoelectronic applications: a theoretical study

We are witnessing a change of paradigm from the conventional top-down to the bottom-up fabrication of nanodevices and particularly optoelectronic devices. A promising example of the bottom-up approach is self-assembling of molecules into layers with predictable and reproducible structural, electronic and optical properties. Nucleobases possess extraordinary ability to self-assembly into one-, two-, and three-dimensional structures. Optical properties of nucleotides are not suitable for wider application to optoelectronics and photovoltaics due to their large optical band gap, which is in contrast to rylene-based dyes that have been intensively investigated in organic optoelectronics. However, these lack the self-assembly capability of nucleobases. Combinations of covalently decorated guanine molecules with rylene type chromophores present 'the best of the both worlds'. Due to the large size of such compounds and its flexible nature their self-assemblies have not been fully understood yet. Here, we use a theoretical approach to study the structural, energetic and optical properties of rylene-based dye decorated guanine (GPDI), as self-assembled on a graphene sheet. Particularly we utilize the density-functional based tight-binding method to study atomic structure of these systems including the potential energy surface of GPDI and stability and organization of single- and multilayered GPDIs on graphene sheet. Using density-functional theory (DFT) we employ the energy decomposition analysis to gain a deeper insight into the contributions of different moieties to stability of GPDI films. Using time dependent DFT we analyze optical properties of these systems. We find that atomically thin films consisting of only a few molecular layers with large surface areas are more favorable than isolated thick islands. Our study of excited states indicates existence of charge separated states similar to ones found in the well-studied hydrogen bonded organic frameworks. The self-assembly characterized with a large homogeneous coverage and long-living charge-separated states provide the great potential for optoelectronic applications.

Naphthalene diimides: perspectives and promise

In this review, we describe the developments in the field of naphthalene diimides (NDIs) from 2016 to the presentday. NDIs are shown to be an increasingly interesting class of molecules due to their electronic properties, large electron deficient aromatic cores and tendency to self-assemble into functional structures. Almost all NDIs possess high electron affinity, good charge carrier mobility, and excellent thermal and oxidative stability, making them promising candidates for applications in organic electronics, photovoltaic devices, and flexible displays. NDIs have also been extensively studied due to their potential real-world uses across a wide variety of applications including supramolecular chemistry, sensing, host-guest complexes for molecular switching devices, such as catenanes and rotaxanes, ion-channels, catalysis, and medicine and as non-fullerene accepters in solar cells. In recent years, NDI research with respect to supramolecular assemblies and mechanoluminescent properties has also gained considerable traction. Thus, this review will assist a wide range of readers and researchers including chemists, physicists, biologists, medicinal chemists and materials scientists in understanding the scope for development and applicability of NDI dyes in their respective fields through a discussion of the main properties of NDI derivatives and of the status of emerging applications.

Highly Stable Single Crystals of Three-Dimensional Porous Oligomer Frameworks Synthesized under Kinetic Conditions

Various robust, crystalline, and porous organic frameworks based on in situ-formed imine-linked oligomers were investigated. These oligomers self-assembled through collaborative intermolecular hydrogen bonding interactions via liquid-liquid interfacial reactions. The soluble oligomers were kinetic products with multiple unreacted aldehyde groups that acted as hydrogen bond donors and acceptors and directed the assembly of the resulting oligomers into 3D frameworks. The sequential formation of robust covalent linkages and highly reversible hydrogen bonds enforced long-range symmetry and facilitated the production of large single crystals, with structures that were unambiguously determined by single-crystal X-ray diffraction. The unique hierarchical arrangements increased the steric hindrance of the imine bond, which prevented attacks from water molecules, greatly improving the stability. The multiple binding sites in the frameworks enabled rapid sequestration of micropollutant in water.

Crystalline supramolecular organic frameworks via hydrogen-bonding between nucleobases

We describe here the first crystalline hydrogen-bonded organic framework made from complementary guanine and cytosine nucleobases.

Towards photoswitchable quadruple hydrogen bonds via a reversible "photolocking" strategy for photocontrolled self-assembly

Developing new photoswitchable noncovalent interaction motifs with controllable bonding affinity is crucial for the construction of photoresponsive supramolecular systems and materials. Here we describe a unique "photolocking" strategy for realizing photoswitchable control of quadruple hydrogen-bonding interactions on the basis of modifying the ureidopyrimidinone (UPy) module with an ortho-ester substituted azobenzene unit as the "photo-lock". Upon light irradiation, the obtained Azo-UPy motif is capable of unlocking/locking the partial H-bonding sites of the UPy unit, leading to photoswitching between homo- and heteroquadruple hydrogen-bonded dimers, which has been further applied for the fabrication of novel tunable hydrogen bonded supramolecular systems. This "photolocking" strategy appears to be broadly applicable in the rational design and construction of other H-bonding motifs with sufficiently photoswitchable noncovalent interactions.

Topological conversion of human telomeric G-quadruplexes from hybrid to parallel form induced by naphthalene diimide ligands

G-quadruplexes (GQs) have become promising anti-cancer therapeutic targets, which are formed by the folding of a guanine-rich repeat DNA/RNA sequence at human telomeres or oncogene promoters. Polymorphism has been observed for the folding topologies of intramolecular GQs. Here we report the topological conversion of human telomeric GQ induced by naphthalene diimide (NDI) ligands in K⁺ solution. The ligands selectively induce metastable hybrid-type GQs to highly stable parallel-type GQ at physiological temperature (37 °C) in dilute aqueous solutions and under crowding conditions that mimic cellular bioenvironment. According to spectroscopic analyses, the topological conversion is speculated to undergo stepwise unfolding of hybrid-type GQ through intermediate states to parallel-type GQ. The results will prompt further studies on the designs of ligands with GQ conformation regulation functions and nanotechnological systems based on nucleic acids with dynamic regulation of GQ conformation.

A novel hydrogen-bonded organic framework for the sensing of two representative organic arsenics

A novel fluorescent hydrogen-bonded organic framework with a double fold interpenetrated structure, HOF-22, has been successfully constructed and structurally characterized. HOF-22 is capable of sensitive detection of two representative organic arsenics from aqueous solution.

Development of Minimal Diguanosinyl Motif toward RNA G-Quadruplex-Like Structures in Solution

Among the non-canonical structures of B-DNA, the G-quadruplex is of particular interest because of its well-defined conformation, high stability, and versatility. Herein we report our studies on the development of an amide-linked minimal diguanosinyl motif that forms a G-quadruplex-like structure in solution in the presence of potassium cations; various linear guanosine amino acid dimers were synthesized with linkers of different chain lengths to investigate the optimum flexibility required to form such structures.

Elucidating Noncovalent Reaction Mechanisms: G-Quartet as an Intermediate in G-Quadruplex Assembly

In analogy to covalent reactions, the understanding of noncovalent association pathways is fundamental to influence and control any supramolecular process. Following an approach that is reminiscent of covalent methodologies, we study here, for the first time, the mechanism of G-quadruplex formation in organic solvents. Our results support a reaction pathway in which the cation shifts the equilibrium towards a G-quartet transient intermediate, which then acts as a template in the formation of the G-quadruplex product.

Hydrogen bonding influences collision-induced dissociation of Na+ -bound guanine tetrads

Na+ -bound guanine (G)-tetrads possess square planar structures formed solely by noncovalent interactions including multiple hydrogen bonds. Unlike G-tetrads facilitated by other alkali metal ions, an intriguing behavior in collision-induced dissociation (CID) has been observed in Na+ -bound G-tetrads, which features a preferential, simultaneous loss of two G ligands in the low energy regime. To understand this unique behavior, we investigated the CID of Na+ -bound G-tetrads with mixed ligands of G and 9-methylguanine (9mG), [Na·Gm ·9mGn ]+ (m + n = 4), and [Li·9mG4 ]+ for comparison. In the CID experiments, the simultaneous losses of two ligands were by far more pronounced than the loss of a single ligand for all five Na+ -bound G-tetrads. However, it appeared that the CID of [Li·9mG4 ]+ prefers to lose single ligands sequentially. An analysis of the fragment abundances suggested that the generation of Na+ -bound dimeric fragments might have occurred with two adjacent ligands. This theoretical study predicted for [Li·9mG4 ]+ that the loss of a single ligand is more energetically favorable than the production of neutral hydrogen-bonded fragments by 35.5 kJ/mol (ΔG). This contradicts our previous calculations for [Na·9mG4 ]+ that a neutral loss of hydrogen-bonded dimers provides the lowest energy product state of Na+ -bound dimeric fragments, which is lower than that of Na+ -bound trimeric fragments by 15.6 kJ/mol. From the results, this comparative study suggests that the pronounced generation of Na+ -bound dimeric fragments in CID of the G-tetrads is likely promoted by the dissociation pathway associated with neutral loss of hydrogen-bonded dimers. It thus demonstrates that multiple hydrogen bonding participating in formation of Na+ -bound G-tetrads may also strongly influence the fate of dissociating complexes of G-tetrads.

Functional Systems Derived from Nucleobase Self-assembly

Dynamic and reversible non-covalent interactions endow synthetic systems and materials with smart adaptive functions that allow them to response to diverse stimuli, interact with external agents, or repair structural defects. Inspired by the outstanding performance and selectivity of DNA in living systems, scientists are increasingly employing Watson-Crick nucleobase pairing to control the structure and properties of self-assembled materials. Two sets of complementary purine-pyrimidine pairs (guanine:cytosine and adenine:thymine(uracil)) are available that provide selective and directional H-bonding interactions, present multiple metal-coordination sites, and exhibit rich redox chemistry. In this review, we highlight several recent examples that profit from these features and employ nucleobase interactions in functional systems and materials, covering the fields of energy/electron transfer, charge transport, adaptive nanoparticles, porous materials, macromolecule self-assembly, or polymeric materials with adhesive or self-healing ability.

Organic Electrode Materials for Metal Ion Batteries

Organic and polymer materials have been extensively investigated as electrode materials for rechargeable batteries because of the low cost, abundance, environmental benignity, and high sustainability. To date, organic electrode materials have been applied in a large variety of energy storage devices, including nonaqueous Li-ion, Na-ion, K-ion, dual-ion, multivalent-metal, aqueous, all-solid-state, and redox flow batteries, because of the universal properties of organic electrode materials. Moreover, some organic materials enable the batteries to be operated in the extreme conditions, such as a wide temperature range (-70 to 150 °C), a wide pH range, and in the presence of O₂. As a guidance for the research in organic batteries, this Review focuses on the reaction mechanisms and applications of organic electrode materials. Six categories of reaction mechanisms and the applications of organic and polymer materials in various rechargeable batteries are discussed to provide an overview of the state-of-the-art organic batteries.

An organic cathode with tailored working potential for aqueous Zn-ion batteries

Up to 0.61 V increase in the working potential was achieved by modifying the anthraquinone (AQ) molecular structure with a stronger electron-withdrawing cyano group.

Real-time Monitoring Excitation Dynamics of Human Telomeric Guanine Quadruplexes: Effect of Folding Topology, Metal Cation, and Confinement by Nanocavity Water Pool

Guanine(G)-rich human telomeric (HT) DNA repeats, crucial to maintenance of genome stability, readily form G-quadruplexes (GQs) with various folding topologies. Research on excitation dynamics of HT-GQs is, however, scarce. Herein, we report a femtosecond time-resolved fluorescence coupled with transient absorption investigation on HT-GQ with the basket-type structure in Na⁺ solution. The result unveils an unusual multichannel nonradiative mechanism dominated by states with varying character of charge transfer lasting ten and hundreds of picoseconds, accounting altogether for an overwhelming ∼85% of the overall deactivation involving proton transfer. Our comparative study shows that encapsulating the GQ in nanocavity water pool or changing it into hydrid-type topologies with the presence of K⁺ ions alter differently energies and lifetimes of these states, yet without affecting the nature of the electronic excitation involved. The finding of this work underscores a leading role of structural rigidity in regulating the interplay with the microenvironment of photoexcited monomolecularly folded HT-GQs.

Strong Enhancement of π-Electron Donor/Acceptor Ability by Complementary DD/AA Hydrogen Bonding

π-Conjugated organic materials possess a wide range of tunable optoelectronic properties which are dictated by their molecular structure and supramolecular arrangement. While many efforts have been put into tuning the molecular structure to achieve the desired properties, rational supramolecular control remains a challenge. Here, we report a novel series of supramolecular materials formed by the co-assembly of weak π-electron donor (indolo[2,3-a]carbazole) and acceptor (aromatic o-quinones) molecules via complementary hydrogen bonding. The resulting polarization creates a drastic perturbation of the molecular energy levels, causing strong charge transfer in the weak donor-acceptor pairs. This leads to a significant lowering (up to 1.5 eV) of the band gaps, intense absorption in the near-IR region, very short π-stacking distances (≥3.15 Å), and strong ESR signals in the co-crystals. By varying the strength of the acceptor, the characteristics of the complexes can be tuned between intrinsic, gate-, or light-induced semiconductivity with a p-type or ambipolar transport mechanism.

Controlled Growth of Ag Nanocrystals in a H-Bonded Open Framework

A procedure that enabled rational access to the first example of hybrid material made of NPs grown within a H-bonded framework is reported. To avoid competitive reactions with the framework units, the metal precursor was chemically trapped in the porous structure and subsequently photo-reduced to afford the hybrid material Ag@SPA-2, which consists of Ag NPs of nanometric sizes (<15 nm) homogeneously distributed in the crystals of the host material. In a subsequent step, taking advantage of the porous matrix the silver NPs have been transformed in situ to Ag₂ S NP by simple infiltration of H₂ S. The supramolecular network is shown to play an important role in stabilizing the inorganic nanomaterials and thus in controlling their growth.

Comparison and Elucidation of Structural Diversity and Variation of G-Rich Sequences with a Single G-Base Difference

Previously, we found the structural diversity of a mitochondrial sequence mt10251 (GGGTGGGAGTAGTTCCCTGCTAAGGGAGGG), including coexistence of a hairpin structure and monomeric, dimeric, and tetrameric G4 structures in 20 mM K⁺ solution. Moreover, a single-base mutation of mt10251 could cause significant changes in terms of structural populations and polymorphism. In this work, we investigate the diverse G4 topologies of mt10251 and structural variation of its mutants. Using circular dichroism (CD), nuclear magnetic resonance (NMR), and polyacrylamide gel electrophoresis (PAGE), we first illustrate an unusual tetrameric G4 structure together with hairpin bulges formed by four strands of mt10251-d30 (GGGTGGGAGTAGTTCCCTGCTAAGGGAGG). Of interest is that the structural conversion from a hairpin structure to diverse G4 structures in mt10251 is negligible in mt10251-d30 after the addition of 20 mM K⁺. Further kinetic and thermal studies of mt10251, mt10251-d30, and their mutants reveal the major factors in determining the transition from a hairpin structure to diverse G4 structures of mt10251 and the structural variation of their mutants after the addition of 20 mM K⁺.

A Three-Dimensional Dynamic Supramolecular "Sticky Fingers" Organic Framework

Engineering high-recognition host-guest materials is a burgeoning area in basic and applied research. The challenge of exploring novel porous materials with advanced functionalities prompted us to develop dynamic crystalline structures promoted by soft interactions. The first example of a pure molecular dynamic crystalline framework is demonstrated, which is held together by means of weak "sticky fingers" van der Waals interactions. The presented organic-fullerene-based material exhibits a non-porous dynamic crystalline structure capable of undergoing single-crystal-to-single-crystal reactions. Exposure to hydrazine vapors induces structural and chemical changes that manifest as toposelective hydrogenation of alternating rings on the surface of the [60]fullerene. Control experiments confirm that the same reaction does not occur when performed in solution. Easy-to-detect changes in the macroscopic properties of the sample suggest utility as molecular sensors or energy-storage materials.