Supramolecular Coordination Research Articles

Strategies to address key challenges of metallacycle/metallacage-based supramolecular coordination complexes in biomedical applications.

Owing to their capacity for dynamically linking two or more functional molecules, supramolecular coordination complexes (SCCs), exemplified by two-dimensional (2D) metallacycles and three-dimensional (3D) metallacages, have gained increasing significance in biomedical applications. However, their inherent hydrophobicity and self-assembly driven by heavy metal ions present common challenges in their applications. These challenges can be overcome by enhancing the aqueous solubility and in vivo circulation stability of SCCs, alongside minimizing their side effects during treatment. Addressing these challenges is crucial for advancing the fundamental research of SCCs and their subsequent clinical translation. In this review, drawing on extensive contemporary research, we offer a thorough and systematic analysis of the strategies employed by SCCs to surmount these prevalent yet pivotal obstacles. Additionally, we explore further potential challenges and prospects for the broader application of SCCs in the biomedical field.

Tetracosanuclear nickel complexes as effective catalysts for cycloaddition of carbon dioxide with epoxides.

A series of well-defined tetracosanuclear nickel complexes 3-7 facilely produced by one-pot synthesis were active catalysts for cycloaddition of CO2 and cyclohexene oxide (CHO). These nickel complexes were doughnut-like supramolecular coordination complexes involving eight repeating units, and each of them contains one Schiff base ligand and three nickel(II) ions. Notably, the 24-nuclear nickel cluster complex 3 in combination with nucleophilic additives was the most efficient catalyst to mediate CO2 coupling with CHO to generate CO2-based cis-cyclohexene carbonates. In addition to CO2/CHO cycloaddition, complex 3 was also found to effectively couple CO2 with other alicyclic epoxides, generating the corresponding cyclic carbonates. Additionally, kinetic investigations for CO2 cycloaddition of CHO using 3 were reported.

Supramolecular palladium complexes based on guanidinium pillar[5]arene for cancer therapy.

The supramolecular palladium complex G-Pd, formed via self-assembly of the Pd-complex of guanidinium pillar[5]arene with Pd2+, was used to encapsulate doxorubicin to form G-Pd@DOX. The nanoparticles exhibit responsiveness to glutathione, controlled drug release, the ability to damage mitochondria, and potent anticancer activity while maintaining low toxicity towards normal cells. This work provides a good example for the application of pillararene-based palladium complexes in cancer therapy and is significant for the discovery of new medicines from supramolecular coordination complexes.

Recent advances in combatting bacterial infections via well-designed metallacycles/metallacages.

Bacterial infections can lead to the development of large-scale outbreaks of diseases that pose a serious threat to human life and health. Also, conventional antibiotics are prone to producing resistance and allergic reactions, and their therapeutic effect is dramatically diminished when bacterial communities form biofilms. Fortunately, well-designed supramolecular coordination complexes (SCCs) have been used as antibacterials or anti-biofilms in recent years. SCCs can kill bacteria by directly engaging with the bacterial surface through electrostatic interactions or by penetrating the bacterial membrane through the auxiliary effect of cell-penetrating peptides. Furthermore, scientists have engineered fluorescent SCCs that can produce reactive oxygen species (ROS) to eliminate bacteria when exposed to laser irradiation, and they also demonstrate outstanding performance in in vivo imaging, enabling integrated diagnosis and treatment. In this review, we summarize the design strategy and applications of SCCs in antibacterials or anti-biofilms and provide an outlook on future research.

Size Control of On-Surface Self-Assembled Nanochains Using Soft Building Blocks.

Owing to their conformational flexibility, soft molecules with side chains play a crucial role in molecular self-assembly or self-organization processes toward bottom-up building of supramolecular nanostructures. However, the influence of the rotating side chains in the confined space and subsequent surface-confined supramolecular self-assembly remains rarely explored. Herein, using the spatial confinement effect between soft building blocks, we realized size control on surface-confined supramolecular coordination self-assembly through the synergy between the repulsive steric hindrance and the attractive chemical interactions. Combining scanning tunneling microscopy with density functional theory calculations and Monte Carlo simulations, we elucidated the effective repulsive force generated by the thermal wiggling motions of the soft building blocks, allowing length tuning of the self-assembled chain structures. Through a delicate balance between the repulsive interaction induced by the spatial confinement effect and the coordinate chemical interaction, we provide a new strategy for controlling the geometry of the on-surface supramolecular nanostructures.

Selectivity, synthesis, crystal structure and biological activity of the anion-coordination phenanthrolinium tartratogermanate

Novel supramolecular cation-anionic coordination compound (HPhen)4[(μ-O){Ge2(OH) (μ-Tart)2}2]·9H2O was synthesised and characterised by the X-ray, elemental, IR- and Hirshfeld surface analysis. It was established that original synthesis method and ability of 1,10-phenanthroline to be protonated promotes the formation of [(μ-O){Ge2(OH)(μ-Tart)2}2]4- anion. In this anion, dimeric fragments are connected by a bridging oxygen atom, and the coordination polyhedra around the germanium atoms adopt a distorted trigonal bipyramidal geometry. The cations HPhen+ serve as effective building blocks, strengthening the overall structure through classical hydrogen bonding and additional π-π stacking interactions. Biological screening of (HPhen)4[(μ-O){Ge2(OH) (μ-Tart)2}2]·9H2O demonstrated its remarkable enzyme-effector and antimicrobial activity. The compounds' efficacy can be attributed to the synergistic effects of the independent cations and anions, as well as the ability of protonated 1,10-phenanthroline to inhibit metal ions in enzymes and form stacking interactions with specific protein components. These characteristics make such compounds highly effective and promising antibacterial agents that minimize the risk of developing bacterial resistance.

Phosphine oxide donor-based dinuclear rhenium(I) metallocycles

Neutral binuclear metallocycles fac- [{Re(CO)3}2(CA)(L)] (1–2) were obtained using Re2(CO)10, flexible ditopic phosphine oxide donor 9,10-bis(dimethylphosphonomethyl)anthracene/ 9,10-bis(diethylphosphonomethyl)anthracene (L), and chloranilic acid (H2−CA) in mesitylene via one-pot solvothermal methods. The metallocycles were characterized by E.A., FT-IR, ESI-MS and NMR analysis. The solid-state structures of 1–2 were confirmed by X-ray analysis which reveal that the complexes adopt binuclear heteroleptic cyclic architectures. The fac- [Re(CO)3] core-based metallocycles 1–2 are two of the very few examples of phosphine oxide donor (P=O)-based supramolecular coordination cyclic complexes.

Dual-Emissive Rectangular Supramolecular Pt(II)-p-Biphenyl with 4,4'-Bipyridine Derivative Metallacycles: Stepwise Synthesis and Photophysical Properties.

Mixed-ligand tetranuclear supramolecular coordination complexes (SCCs) of Pt(II)-p-biphenyl and bridging ligands derivatives of 4,4'-bypiridine (8)-(10), were synthesized and characterized. The SCCs were synthesized stepwise, starting from the Pt-p-biphenyl -Pt core. The crystal structure of complex {[Pt(2,2'-bpy)]4(μ-bph)2(μ-(4,4'-bpy)2}{PF6}4 (2,2'-bpy = 2,2'-bipyridine, bph = p-biphenyl and 4,4'-bpy = 4,4' bipyridine), was determined using single-crystal diffraction methods. The emission profile of the tetranuclear complexes (8)-(10) was influenced by the length of the bridging ligands and was found to depend on solvent polarity. Dual-emission patterns in methanol-water mixtures were observed only in the cases of complexes (9) and (10), attributed to aggregation-induced emission phenomena.

Spin Qubit in a 2D GdIII NaI -Based Oxamato Supramolecular Coordination Framework.

Qubits are the basic unit of quantum information and computation. To realize quantum computing and information processing, the decoherence times of qubits must be long enough. Among the studies of molecule-based electron spin qubits, most of the work focused on the ions with the spin S=1/2, where only single-bit gates can be constructed. However, quantum operations require the qubits to interact with each other, so people gradually carry out relevant research in ions or systems with S>1/2 and multilevel states. In this work, a two-dimensional (2D) oxygen-coordinated GdIII NaI -based oxamato supramolecular coordination framework, Na[Gd(4-HOpa)4 (H2 O)] ⋅ 2H2 O (1, 4-HOpa=N-4-hydroxyphenyloxamate), was selected as a possible carrier of qubit. The field-induced slow magnetic relaxation shows this system has phonon bottleneck (PB) effect at low temperatures with a very weak magnetic anisotropy. The pulse electron paramagnetic resonance studies show the spin-lattice and spin-spin relaxation times are T1 =1.66 ms at 4 K and Tm =4.25 μs at 8 K for its diamagnetically diluted sample (1Gd0.12 %). It suggested that the relatively long decoherence time is mainly ascribed to its near isotropic and the PB effect from resonance phonon trapped for pure sample, while the dilution further improves its qubit performance.

Fe doped Mo-Ni supramolecular coordination polymer based bifunctional oxygen electrocatalyst with high efficiency and duration for rechargeable zinc-air battery

In the present area of electrochemistry, due to the scarcity and unavailability of precious metals, it is a great challenge and a new opportunity to develop bifunctional electrocatalysts for zinc-air batteries (ZABs) with high activity, low cost and strong durability. In this study, an excellent electrocatalyst (Fe@MoNi/NCP-800) for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was successfully prepared by pyrolyzing Fe2+ ion doped bimetallic Mo-Ni supramolecular coordination polymer (SCP) at 800 °C with carbon paper (CP) as self-supporting material. Owing to its unique FeNi alloy nanotube structure supported by the in situ formed MoN and the trimetallic synergies, the as-obtained electrocatalyst showed superior catalytic performance to that of commercial Pt/C half-wave potential (E1/2) of 0.846 V and RuO2 overpotential (η) of 300 mV. In addition, the ZABs prepared with Fe@MoNi/NCP-800 has a small charge–discharge voltage gap of 0.85 V, high energy efficiency of 35.25% and excellent cycle performance (308 h) at 10 mA cm−2. This research provides a very promising transition-metal alloy multifunctional electrocatalyst for the development of ZABs with high efficiency and duration, and a meaningful idea for the future rational design and synthesis of new coordination polymer or supramolecular coordination polymer-based electrocatalysts.

Reversible and Turn-On Fluorescence Detection of Phosphate in Aqueous Solution and Living Cell Imaging by Supramolecular Metallacycles with AIE-Active Ligands.

Luminescent supramolecular metallacycles have attracted great interest as a new promising class of sensing substrates. In this work, two tetraphenylethene (TPE)-based diimidazole and dipyrazole ligands with the aggregation-induced emission (AIE) feature were designed for the construction of supramolecular tetragonal metallacycles 1-4 with two 90° mononuclear [(bpy)M]2+ or dinuclear [(bpy)2M2]4+ acceptors (bpy = 2,2'-dipyridine; M = Pd, Pt), in which the fluorescence can be quenched to an "off" state due to the ligand-to-metal charge transfer (LMCT). Metallacycle 1 was utilized as a fluorescence sensor for phosphate (PO43-) detection in aqueous solution by means of disassembly, leading to the release of the ligand. Additionally, the metallacycle can be regenerated through self-assembly via the introduction of Pd(II) acceptors. PO43- was detected using TPE-based metallacycles over a wide concentration range, with a detection limit as low as 2.1 × 10-8 M. Furthermore, sensor 1 also presented the semiquantitative visual detection ability for PO43- in the test paper mode via fluorescence changes. The aforementioned studies not only enhance the current research on fluorescent materials but also offer a strategy for the creation of stimuli-responsive supramolecular coordination complexes.

Synthesis of 177Lu-Labeled, Somatostatin-2 Receptor-Targeted Metalla-Assemblies: Challenges in the Design of Supramolecular Radiotherapeutics.

Self-assembled supramolecular coordination complexes (SCCs) hold promise for biomedical applications in cancer therapy, although their potential in the field of nuclear medicine is still substantially unexplored. Therefore, in this study an exo-functionalized cationic [Pd2L2]4+ metallacycle (L = 3,5-bis(3-ethynylpyridine)phenyl), targeted to the somatostatin-2 receptor (sst2R) and featuring the DOTA chelator (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) in order to bind the β-- and γ-emitter lutetium-177, was synthesized by self-assembly following ligand synthesis via standard solid-phase peptide synthesis (SPPS). This metallacycle was then characterized by reverse-phase high-performance liquid chromatography (RP-HPLC), electrospray ionization mass spectrometry (ESI-MS), and 1H and 1H-DOSY NMR (DOSY = diffusion-ordered spectroscopy). A procedure for the radiolabeling of the metallacycle with 177Lu was also optimized. The resulting [nat/177Lu]Lu-DOTA-metallacycle, termed [nat/177Lu]Lu-Cy, was evaluated concerning its stability and in vitro properties. The compound was more lipophilic compared to the reference [177Lu]Lu-DOTA-TATE (logPOct/H2O = -0.85 ± 0.10 versus -3.67 ± 0.04, respectively). While [natLu]Lu-Cy revealed low stability in a DMEM/F12 GlutaMax medium, it demonstrated good stability in other aqueous media as well as in DMSO. A high sst2R binding affinity (expressed as IC50) was determined in CHOsst2 cells (Chinese hamster ovary cells that were stably transfected with human sst2R). Moreover, the metallacycle exhibited high human serum albumin binding, as assessed by high-performance affinity chromatography (HPAC), and moderate stability in human serum compared to [177Lu]Lu-DOTA-TATE (TATE = (Tyr3)-octreotate). In order to improve stability, a heteroleptic approach was used to develop a less sterically hindered cage-like SCC that is potentially endowed with host-guest chemistry capability, which has been preliminarily characterized by RP-HPLC and ESI-MS. Overall, our initial results encourage future studies on sst2R-directed SCCs and have led to new insights into the chemistry of ss2R-directed SCCs for radiopharmaceutical applications.

Hydrogen-bonded supramolecular structures in copper(II) nitrobenzoates with N-methylnicotinamide: synthesis, supramolecular structure, Hirshfeld surface analysis, spectral and DFT study

The synthesis of six new copper(II) nitrobenzoate complexes with N-methylnicotinamide, used as an auxiliary ligand for a supramolecular interaction study, is reported. Crystal structures of six novel compounds [Cu(2-NO2bz)2(mna)2(H2O)2] (1), [Cu(2-NO2bz)2(mna)2(H2O)2]∙2H2O (2), [Cu(3-NO2bz)2(mna)2(H2O)2] (3), [Cu(3,5-(NO2)2bz)2(mna)2(H2O)2]∙2H2O (4), [Cu(4-NO2bz)2(mna)2(H2O)2]∙2(4-NO2bzH) (5) and [Cu(3,5-(NO2)2bz)2(mna)(H2O)3] (6) (mna = N-methylnicotinamide, 2-NO2bz = 2-nitrobenzoate, 3-NO2bz = 3-nitrobenzoate, 4-NO2bz = 4-nitrobenzoate, 3,5-(NO2)2bz = 3,5-dinitrobenzoate) were determined by X-ray analysis. Compounds 1–6 are mononuclear with a tetragonal-bipyramidal geometry around the Cu2+ ion. The molecules of the studied complexes are mostly linked by a combination of N–H…O and O–H…O hydrogen bonds between N-methylnicotinamide and water molecules into supramolecular hydrogen-bonded coordination chains and networks. Intermolecular interactions in the supramolecular structures were also studied using Hirshfeld surface analysis. In addition, the complexes 1–6 have been characterised by elemental analysis, IR, UV–Vis and EPR spectroscopy. Density functional theory calculations were performed in order to reproduce the EPR magnetic parameters. DFT calculations of the EPR parameters show a good agreement with the experimental results.

Two New Coordination Polymers Based on Viologen Ligands: Synthesis, Photochromism and Ammonia Sensing

Synthesized two supramolecular coordination polymers, {Cd3[(bcbpy)3Cl6]·8H2O}n (1) (bcbpy=1,1′-bis(3-carboxybenzyl)-4,4′-bipyridinium) and {Zn[(bcbpy)0.5(nip)]·H2O}n (2) (nip2-=5-nitroisophthalic acid anion), showed good photochromic properties when both coordination polymers changed from yellow to dark green under light stimulation, and the primary color could be restored at 85-95 ℃ for 60 min, this reversible cycle can be repeated more than 5 times. This photochromism is caused by photoinduced electron transfer to viologen free radicals. In addition, in ammonia vapor, both complexes changed from yellow to tan, showing good ammonia sensing characteristics. Research has found that complexes 1 and 2 exhibit sensing differences, with a response rate to light of 2>1. This sensing difference is mainly related to the D-A distance between molecules, π-π interactions, and the regulatory effect of metal ions or secondary ligands.

Ultrastretchable, repairable and highly sensitive xanthan collagen nanosilver hydrogel for wide temperature flexible sensing

Conductive hydrogels, lauded for their electrical conductivity, precise information capture, biocompatibility, and extensibility, have gained prominence as ideal candidate materials for flexible wearable sensor applications. Nevertheless, these sensors must surmount numerous challenges such as environmental temperature variations, bacterial growth in high-humidity environments, low signal detection sensitivity, irreversible damage, and mechanical performance stability during use. In response to these challenges, we present a hydrophobic supramolecular and dynamic coordination double-network hydrogel, prepared through a solvent-exchange method, with an accelerated gelation rate. The coordination of dynamic hydrogen bonds and coordination bonds within the hydrophobic supramolecular network imbues the hydrogel with superior mechanical properties (elongation at break around 4900%, tensile strength approximately 506 kPa) and improved self-healing capabilities. This solvent-exchange-mediated hydrogel exhibits broad temperature resilience (−20–60 °C) and reliable repeatability. Additionally, the sensor enables wireless human signal monitoring with a rapid response time (75 ms) and heightened sensitivity (gauge factor = 22.34). The wearable sensor’s antibacterial efficacy effectively suppresses bacterial propagation in high-moisture hydrogels, with a bacterial inhibition rate of 99.9%. The findings from our series of studies reveal the successful fabrication of stable, flexible wearable sensors with self-healing, antibacterial, high sensitivity, and broad temperature tolerance characteristics, showcasing the immense potential for applications in wearable electronics, wireless monitoring, and human–machine interactions.

Quinolyl-Based PGM Metallarectangles: Antiproliferative Activity, DNA and BSA Protein Interactions, and a Molecular Docking Perspective.

The increased success of small metal-containing molecules as pharmaceutical agents has prompted investigations into the pharmacological activity of a different class of metal-based compounds; supramolecular coordination complexes (SCCs). Such complexes have been extensively investigated for their anticancer activity, with many displaying activities comparable or superior to available clinical chemotherapeutic drugs. Here, we evaluated a series of quinoline-containing binuclear complexes and metallarectangles for their in vitro anticancer activity in the hormone receptor positive MCF-7 and triple negative MDA-MB-231 breast cancer cell lines. The preliminary cytotoxic screen, in the MCF-7 cell line, revealed that the ligand (7-chloro-4-(pyridin-4-yl)quinoline, L) and metallarectangle [{Ir(μ-Cl)(Cp*)}4 (μ-L)2 ](OTf)4 display superior activity to cisplatin, while [{Ru(p-cymene)}4 (μ-η2 -η2 -C2 O4 )2 (μ-L)2 ](OTf)4 was more potent than cisplatin in the triple-negative MDA-MD-231 cell line. Upon evaluation in a multidose screen, ligand L and metallarectangle [{Ir(μ-Cl)(Cp*)}4 (μ-L)2 ](OTf)4 displayed antiproliferative activity almost two-fold greater than cisplatin in the MCF-7 cell line, while [{Ru(p-cymene)}4 (μ-η2 -η2 -C2 O4 )2 (μ-L)2 ](OTf)4 was over two-times more active than cisplatin in the MDA-MB-231 cell line. Additionally, using the non-tumorigenic MCF-12 A breast epithelial cell line, the compounds demonstrate increased selectivity toward breast cancer cells over non-tumorigenic cells. Furthermore, investigations into the interactions of ligand L and selected complexes with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) indicate favourable binding.

Regulating the solvation sheath of zinc ions by supramolecular coordination chemistry toward ultrastable zinc anodes

AbstractAqueous zinc‐ion batteries (ZIBs) have attracted extensive interest for the next‐generation batteries, which, however, are facing great challenges due to the poor reversibility of zinc (Zn) anodes and side reactions of water decomposition. Herein, we demonstrated a strategy that the solvation sheath of Zn ions could be facilely regulated by supramolecular coordination chemistry by adding small amounts of cyclodextrins (CDs) and, hence, inhibited the side reactions and side products, widened the electrochemical window, facilitated the homogenous deposition of Zn ions, refined the Zn grains, and enhanced the stability of Zn anodes. Importantly, we demonstrated that compared with α‐ and β‐CD, the γ‐CD showed the best regulation effect of the solvation sheath of Zn ions either at the same molar ratio or at the same mass concentration, which could be ascribed to their difference in supramolecular coordination chemistry and the strongest interaction of γ‐CD with Zn ions. As a result, with γ‐CD, the Zn//Zn symmetric cells showed ultrahigh stability with a cycling lifespan of over 2400 h at a current density of 1 mA/cm2. These results highlight the regulation of solvation sheath by supramolecular coordination chemistry for highly stable Zn anodes and pave a new way to realize high‐performance ZIBs.

Organometallic-Organic Hybrid Assemblies Featuring the Diantimony Complex [Cp2Mo2(CO)4(μ,η2-Sb2)], Ag(I) Ions and Ndonor Molecules as Building Blocks.

The reactions of the of the organometallic ligand complex [Cp2Mo2(CO)4(μ,η2-Sb2)] (C) with Ag[TEF] ([TEF]‾ = [Al{OC(CF3)3}4]‾) in the presence of a number of di- or polytopic N-donor molecules (1,6,7,12-tetraazaperylene (L1), 2,2'-bipyrimidine (L2), 4,4'-bipyridine (L3), trans-1,2-di(4-pyridyl)ethylene (L4)) and 1,3-di(4-pyridyl)propane (L5), were studied. These reactions lead, depending on the reaction stoichiometry and choice of linker, to the selective formation of dimeric or tetrameric supramolecular coordination complexes as well as 1D and 2D coordination polymers (CPs). The presented compounds are unique examples of supramolecular complexes incorporating both organometallic Sb-donor and organic N-donor molecules as ligands to stabilize metal ions. Moreover, one of the formed compounds, the CP [Ag4(η2:1-C)4(L4)4]n[TEF]4n, represents an exceptional 1D polymer incorporating both N- and Sb-donor ligands as connectors for metal ions.

High-internal phase Pickering emulsion stabilized by crystals of nobiletin: assembly of supramolecular metal-polyphenolic coordination complexes for surface coating.

High internal phase Pickering emulsion has attracted extensive attention due to its unique properties, and has broad application prospects in the food field, such as as a fat replacer, packaging and delivery of nutrients or probiotics, and 3D printing of food. However, efficient and edible high-internal phase Pickering stabilizer is still a persistent challenge for food scientists. Herein, the nobiletin (NOB) was selected as a model substance, the particle physicochemical properties (droplet size, rheological behavior, and transmission profile) showed that supramolecular metal-polyphenolic coordination networks could suppress the ripening and growth of crystals on the oil-water interface. When the ratio of tannic acid (TA) and Fe3+ was 3:1, the crystallization growth of NOB could be effectively inhibited. Due to the reduction of energy steric hindrance in the adsorption process, the resulting NOB-TA3 -Fe3+ 1 (NT3 Fe1 ) nanoparticles had the greatest potential to extend emulsion storage time. This particle could stabilise a high-internal phase emulsion, of which the oil phase was 80%, for at least 30 days and eventually lead to high system viscosity. The findings in this work provided a novel selection of healthy emulsifiers as well as an effective emulsion delivery system for hydrophobic and crystalline nutrients. This article is protected by copyright. All rights reserved.

Topological effect on fluorescence emission of tetraphenylethylene-based metallacages

Herein, we describe the selective formation of a barrel-shaped or a ball-shaped fluorescent metallacage by controlling the shape and stoichiometry of the building blocks. Specifically, the tetraphenylethylene-based donor and two acceptors with different numbers of Pt(II) centers were combined via coordination-driven self-assembly. Owing to the differences in the shapes of the assemblies, the resultant ball-shaped metallacage displayed stronger and blue-shifted fluorescence compared to the barrel-shaped one in dilute solutions, while a reversal of fluorescence intensities was observed in the aggregation process. Overall, this work demonstrates that the photophysical properties of supramolecular coordination complexes can be affected by subtle geometrical factors, which can be controlled precisely at the molecular level.