Coordination Cages Research Articles

A stable biocompatible porous coordination cage promotes in vivo liver tumor inhibition

A stable biocompatible porous coordination cage promotes in vivo liver tumor inhibition

Long-Lived C60 Radical Anion Stabilized Inside an Electron-Deficient Coordination Cage.

Fullerene C60 and its derivatives are widely used in molecular electronics, photovoltaics, and battery materials, because of their exceptional suitability as electron acceptors. In this context, single-electron transfer on C60 generates the C60• - radical anion. However, the short lifetime of free C60• - hampers its investigation and application. In this work, we dramatically stabilize the usually short-lived C60• - species within a self-assembled M2L4 coordination cage consisting of a triptycene-based ligand and Pd(II) cations. The electron-deficient cage strongly binds C60 by providing a curved inner π-surface complementary to the fullerene's globular shape. Cyclic voltammetry revealed a positive potential shift for the first reduction of encapsulated C60, which is indicative of a strong interaction between confined C60• - and the cationic cage. Photochemical one-electron reduction with 1-benzyl-1,4-dihydronicotinamide allows selective and quantitative conversion of the confined C60 molecule in millimolar acetonitrile solution at room temperature. Radical generation was confirmed by nuclear magnetic resonance, electron paramagnetic resonance, ultraviolet-visible-near-infrared spectroscopy and electrospray ionization mass spectrometry. The lifetime of C60• - within the cage was determined to be so large that it could still be detected after one month under an inert atmosphere.

Synthesis and Structure of the Bis- and Tris-Polyhedral Hybrid Carboranoclathrochelates with Functionalizing Biorelevant Substituents-The Derivatives of Propargylamine Iron(II) Clathrochelates with Terminal Triple C≡C Bond(s).

A synthetic strategy for obtaining structurally flexible hybrid iron(II) carboranoclatrochelates functionalized with biorelevant groups, based on a combination of a 1,3-dipolar cycloaddition reaction with nucleophilic substitution of an appropriate chloroclathrochelate precursor, was developed. In its first stage, a stepwise substitution of the dichloroclathrochelate precursor with amine N-nucleophiles of different natures in various solvents was performed. One of its two chlorine atoms with morpholine or diethylamine in dichloromethane gave reactive monohalogenoclathrochelate complexes functionalized with abiorelevant substituents. Further nucleophilic substitution of their remaining chlorine atoms with propargylamine in DMF led to morpholine- and diethylamine-functionalized monopropargylamine cage complexes, the molecules of which contain the single terminal C≡C bond. Their “click” 1,3-cycloaddition reactions in toluene with ortho-carborane-(1)-methylazide catalyzed by copper(II) acetate gave spacer-containing di- and tritopic iron(II) carboranoclatrochelates formed by a covalent linking between their different polyhedral(cage) fragments. The obtained complexes were characterized using elemental analysis, MALDI-TOF mass, UV-Vis, 1H, 1H{11B}, 11B, 11B{1H}, 19F{1H} and 13C{1H}-NMR spectra, and by a single crystal synchrotron X-ray diffraction experiment for the diethylamine-functionalized iron(II) carboranoclathrochelate. Its encapsulated iron(II) ion is situated almost in the center of the FeN6-coordination polyhedron possessing a geometry intermediate between a trigonal prism and a trigonal antiprism with a distortion angle φ of approximately 28°. Conformation of this hybrid molecule is strongly affected by its intramolecular dihydrogen bonding: a flexibility of the carborane-terminated ribbed substituent allowed the formation of numerous C–H…H–B intramolecular interactions. The H(C) atom of this carborane core also forms the intermolecular C–H…F–B interaction with an adjacent carboranoclathrochelate molecule. The N–H…N intermolecular interaction between the diethylamine group of one hybrid molecule and the heterocyclic five-membered 1H-[1,2,3]-triazolyl fragment of the second molecule of this type caused formation of H-bonded carboranoclathrochelate dimers in the X-rayed crystal.

Modulating Structural and Electronic Properties of Rare Archimedean and Johnson-Type Mn Cages.

High-nuclearity Mn complexes have attracted significant scientific attention due to their fascinating magnetic properties and their relevance to bioinorganic systems and catalysis. In this work, we demonstrate how the strong binding characteristics of phosphonate ligands can be coupled with sterically hindered carboxylate groups to influence the symmetry of Mn coordination clusters. We describe the structure of two high-nuclearity Mn coordination cages, {Mn12} and {Mn15}, synthesized using this approach. These cages are structurally related to the truncated tetrahedral geometry and adopt rare topological features of Archimedean and Johnson-type solids. Their structural attributes distinctively influence their magnetic properties and electrocatalytic H2O oxidation characteristics.

Exploring the Ion Solvation Environments in Solid-State Polymer Electrolytes through Free-Energy Sampling

Lithium-ion batteries are high energy density power sources that find uses in the automobile industry for electric cars and various portable devices like smartphones, laptops etc. There are strong motivations for developing solid-state electrolytes due to safety concerns associated with the combination of flammable liquid electrolytes and cell shorting due to lithium dendrite growth in current technology. A major issue with solid electrolytes is their low conductivity, which limits the power density (rate of charge/discharge), and possible loss of electrical contact due to anode shrinking. Lithium salts dissolved in poly(ether-acetals) are prime candidates for such electrolytes but the major challenge in improving the performance of these batteries is that the exact mechanism of the motion of the Li+ ions in such systems is not yet well understood. Our goal is to understand the underlying structural differences in the lithium coordination environments in these different systems and how this would affect the movement of the lithium ion from one coordination cage to another. This insight will allow us to suggest new compositions for electrolytes with improved performance for battery applications.Molecular dynamics simulations using newly developed, accurate interaction potentials have helped elucidate possible mechanisms for various transport properties in these systems. The presence of a second coordination shell around the Li ion, observed in some of these systems, seems to distort the first coordination shell, creating a more open cage structure that may help facilitate transport in these polymers. Furthermore, this distorted coordination may also assist in the formation of a lower coordination transition state while the Li ions jump from one cage to another during diffusion. This may be similar to the pathways followed in solid-state transport - either during topotactic intercalation, as ions move from interstitial to interstitial site; or within materials with solid-solid phase transitions related to thermally induced rotations of complex anions. Free energy calculations further elucidate the relative stability of these different Li-ether coordination environments and the possible pathways to move between them (See figure 1 for example). Furthermore, to understand the associated correlations of glass transition temperature in these systems with microscopic chemical details like the polymer backbone chemistry, ion clustering and coordination, we study the trends in these different systems with extensive statistics from long time molecular dynamics simulations at different temperatures and compositions. Figure 1

Synthesis, crystal structure and photocurrent response property of a copper(II)-organic supramolecular coordination compound based on [Cu4(phen)4(OH)4(H2O)2]4+ cations and [Cu(EDTA)]2− anions

A hydrogen-bonded hexanuclear cluster-based supramolecular coordination compound {[Cu4(phen)4(OH)4(H2O)2][Cu(EDTA)]2·14H2O}n (1) (phen = 1, 10-phenanthroline, EDTA4- = full deprotonated ethylenediamine tetraacetic acid) has been isolated through the self-assembly of aromatic diimine ligand phen and sexadentate ligand EDTA4- with acetate copper(II). The [Cu4(phen)4(OH)4(H2O)2][Cu(EDTA)]2·14H2O unit contains a centrally chair-like stepped hydroxy-bridged tetranuclear [Cu4(phen)4(OH)4(H2O)2]4+ cationic cluster, two opposite EDTA4- chelated mononuclear [Cu(EDTA)]2- coordination anions, and fourteen free water molecules. The discrete [Cu4(phen)4(OH)4(H2O)2][Cu(EDTA)]2·14H2O unit is extended to a 3D supramolecular structure {[Cu4(phen)4(OH)4(H2O)2][Cu(EDTA)]2·14H2O}n (1) by van der Waals interactions and hydrogen bonds. The structure of 1 has been defined by single crystal X-ray diffractometer (SCXRD), and well-characterized by a series of technologies, such as infrared spectroscopy, thermogravimetric analysis, and UV–Vis absorption spectroscopy and diffuse reflectance spectroscopy. In addition, the photocurrent response, electrochemistry and luminescence properties have also been investigated.

An Octa-Urea [Pd2 L4 ]4+ Cage that Selectively Binds to n-octyl-α-D-Mannoside.

Designing compounds for the selective molecular recognition of carbohydrates is a challenging task for supramolecular chemists. Macrocyclic compounds that incorporate isophtalamide or bisurea spacers linking two aromatic moieties have proven effective for the selective recognition of all‐equatorial carbohydrates. Here, we explore the molecular recognition properties of an octa‐urea [Pd2L4]4+ cage complex (4). It was found that small anions like NO3 − and BF4 − bind inside 4 and inhibit binding of n‐octyl glycosides. When the large non‐coordinating anion ‘BArF’ was used, 4 showed excellent selectivity towards n‐octyl‐α‐D‐Mannoside with binding in the order of K a≈16 M−1 versus non‐measurable affinities for other glycosides including n‐octyl‐β‐D‐Glucoside (in CH3CN/H2O 91 : 9).

Tuning the Size and Geometry of Heteroleptic Coordination Cages by Varying the Ligand Bent Angle.

Spherical assemblies of the type [Pdn L2n ]2n+ can be obtained from PdII salts and curved N-donor ligands, L. It is well established that the bent angle, α, of the ligand is a decisive factor in the self-assembly process, with larger angles leading to complexes with a higher nuclearity, n. Herein, we report heteroleptic coordination cages of the type [Pdn Ln L'n ]2n+ , for which a similar correlation between the ligand bent angle and the nuclearity is observed. Tetranuclear cages were obtained by combining [Pd(CH3 CN)4 ](BF4 )2 with 1,3-di(pyridin-3-yl)benzene and ligands featuring a bent angle of α=120°. The use of a dipyridyl ligand with α=149° led to the formation of a hexanuclear complex with a trigonal prismatic geometry; for linear ligands, octanuclear assemblies of the type [Pd8 L8 L'8 ]16+ were obtained. The predictable formation of heteroleptic PdII cages from 1,3-di(pyridin-3-yl)benzene and different dipyridyl ligands is evidence that there are entire classes of heteroleptic cage structures that are privileged from a thermodynamic point of view.

Mechanochemical Release of Non-Covalently Bound Guests from a Polymer-Decorated Supramolecular Cage.

Supramolecular coordination cages show a wide range of useful properties including, but not limited to, complex molecular machine‐like operations, confined space catalysis, and rich host–guest chemistries. Here we report the uptake and release of non‐covalently encapsulated, pharmaceutically‐active cargo from an octahedral Pd cage bearing polymer chains on each vertex. Six poly(ethylene glycol)‐decorated bipyridine ligands are used to assemble an octahedral PdII 6(TPT)4 cage. The supramolecular container encapsulates progesterone and ibuprofen within its hydrophobic nanocavity and is activated by shear force produced by ultrasonication in aqueous solution entailing complete cargo release upon rupture, as shown by NMR and GPC analyses.

A Cavity-Tailored Metal-Organic Cage Entraps Gases Selectively in Solution and the Amorphous Solid State.

Here we report the subcomponent self‐assembly of a truxene‐faced Zn4L4 tetrahedron, which is capable of binding the smallest hydrocarbons in solution. By deliberately incorporating inward‐facing ethyl groups on the truxene faces, the resulting partially‐filled cage cavity was tailored to encapsulate methane, ethane, and ethene via van der Waals interactions at atmospheric pressure in acetonitrile, and also in the amorphous solid state. Interestingly, gas capture showed divergent selectivities in solution and the amorphous solid state. The selective binding may prove useful in designing new processes for the purification of methane and ethane as feedstocks for chemical synthesis.

Linear Free Energy Relationships for Enzymatic Reactions: Fresh Insight from a Venerable Probe.

ConspectusLinear free energy relationships (LFERs) for substituent effects on reactions that proceed through similar transition states provide insight into transition state structures. A classical approach to the analysis of LFERs showed that differences in the slopes of Brønsted correlations for addition of substituted alkyl alcohols to ring-substituted 1-phenylethyl carbocations and to the β-galactopyranosyl carbocation intermediate of reactions catalyzed by β-galactosidase provide evidence that the enzyme catalyst modifies the curvature of the energy surface at the saddle point for the transition state for nucleophile addition. We have worked to generalize the use of LFERs in the determination of enzyme mechanisms. The defining property of enzyme catalysts is their specificity for binding the transition state with a much higher affinity than the substrate. Triosephosphate isomerase (TIM), orotidine 5′-monophosphate decarboxylase (OMPDC), and glycerol 3-phosphate dehydrogenase (GPDH) show effective catalysis of reactions of phosphorylated substrates and strong phosphite dianion activation of reactions of phosphodianion truncated substrates, with rate constants kcat/Km (M–1 s–1) and kcat/KdKHPi (M–2 s–1), respectively. Good linear logarithmic correlations, with a slope of 1.1, between these kinetic parameters determined for reactions catalyzed by five or more variant forms of each catalyst are observed, where the protein substitutions are mainly at side chains which function to stabilize the cage complex between the enzyme and substrate. This shows that the enzyme-catalyzed reactions of a whole substrate and substrate pieces proceed through transition states of similar structures. It provides support for the proposal that the dianion binding energy of whole phosphodianion substrates and of phosphite dianion is used to drive the conversion of these protein catalysts from flexible and entropically rich ground states to stiff and catalytically active Michaelis complexes that show the same activity toward catalysis of the reactions of whole and phosphodianion truncated substrates. There is a good linear correlation, with a slope of 0.73, between values of the dissociation constants log Ki for release of the transition state analog phosphoglycolate (PGA) trianion and log kcat/Km for isomerization of GAP for wild-type and variants of TIM. This correlation shows that the substituted amino acid side chains act to stabilize the complex between TIM and the PGA trianion and that ca. 70% of this stabilization is observed at the transition state for substrate deprotonation. The correlation provides evidence that these side chains function to enhance the basicity of the E165 side chain of TIM, which deprotonates the bound carbon acid substrate. There is a good linear correlation, with a slope of 0.74, between the values of ΔG‡ and ΔG° determined by electron valence bond (EVB) calculations to model deprotonation of dihydroxyacetone phosphate (DHAP) in water and when bound to wild-type and variant forms of TIM to form the enediolate reaction intermediate. This correlation provides evidence that the stabilizing interactions of the transition state for TIM-catalyzed deprotonation of DHAP are optimized by placement of amino acid side chains in positions that provide for the maximum stabilization of the charged reaction intermediate, relative to the neutral substrate.

Enhanced linear and non-linear optical activity of lead onto l-threonine cadmium acetate crystal

Herein, we describe the growth and characterization of new crystal lead-doped l-threonine cadmium acetate (LTCA). The supramolecular coordination compounds are crystallized by slow evaporation technique at ambient temperature. The X-ray diffraction techniques confirm monoclinic crystal system. The presence of lead and the LTCA lattices were identified using EDAX analysis. l-Threonine amino acids have unique properties like zwitterionic nature and molecular chirality, which improve the optical properties of the lead-doped crystal. The linear optical parameters such as optical band gap and refractive indexes are estimated at lower cutoff wavelength from UV–Vis analysis. The variation of dielectric constant, dielectric loss with frequency is studied using LCR meter. Due to the electropositive character of lead the static permittivity increases. Magnetic behavior changes to paramagnetic nature due to the inclusion of lead. TG/DTA analysis suggests that the crystal is thermally stable up to 135.32 °C. Using Nd-YAG laser, the NLO property was studied and the lead-doped LTCA crystal shows higher SHG efficiency than the LTCA crystal.

Stabilizing Porosity in Organic Cages through Coordination Chemistry.

The number of studies concerning the permanent porosity of molecular materials, especially porous organic cages (POCs) and porous coordination cages (PCCs), have increased substantially over the past decade. The work presented here outlines novel approaches to the preparation of porous molecular structures upon metalation of nonporous, amine-based organic cages. Reduction of the well-known CC3 and CC1 imine-based POCs affords nonporous, highly flexible amine cages. These materials can be endowed with significant levels of structural rigidity via post-synthetic metalation of their ethylenediamine-type binding pockets. The hybrid metal-organic cages accessed through this approach combine aspects of POC and PCC chemistry, with structures of this type providing a potentially promising new direction for the design and development of porous molecular materials with tunability in overall charge, metal cation, porosity, and solubility.

Inside Cover: Mechanochemical Release of Non‐Covalently Bound Guests from a Polymer‐Decorated Supramolecular Cage (Angew. Chem. Int. Ed. 24/2021)

A supramolecular coordination cage in the center of a star-shaped water-soluble polymer responds to ultrasonication-induced shear force in solution. As reported by Robert Göstl, Bernd M. Schmidt, and co-workers in their Communication on page 13626, the octahedral Pd cage (blue panels) bearing polymer chains (red) on each vertex (metallic) encapsulates pharmaceutically active cargo within its hydrophobic nanocavity and is activated by sonication in aqueous solution, with complete cargo release upon rupture.

Superparamagnetic iron oxide–gold nanoparticles conjugated with porous coordination cages: Towards controlled drug release for non-invasive neuroregeneration

This paper reports a smart intracellular nanocarrier for sustainable and controlled drug release in non-invasive neuroregeneration. The nanocarrier is composed by superparamagnetic iron oxide-gold (SPIO-Au) core-shell nanoparticles (NPs) conjugated with porous coordination cages (PCCs) through the thiol-containing molecules as bridges. The negatively charged PCC-2 and positively charged PCC-3 are compared for intracellular targeting. Both types result in intracellular targeting via direct penetration across cellular membranes. However, the pyrene (Py)-PEG-SH bridge enabled functionalization of SPIO-Au NPs with PCC-3 exhibits higher interaction with PC-12 neuron-like cells, compared with the rhodamine B (RhB)-PEG-SH bridge enabled case and the stand-alone SPIO-Au NPs. With neglectable toxicities to PC-12 cells, the proposed SPIO-Au-RhB(Py)-PCC-2(3) nanocarriers exhibit effective drug loading capacity of retinoic acid (RA) at 13.505 μg/mg of RA/NPs within 24 h. A controlled release of RA is achieved by using a low-intensity 525 nm LED light (100% compared to 40% for control group within 96 h).

Separation of the host-guest system for ferrocene derivatives in octahedral nanocages by electrochemical ionization

An octahedral nanosized M6L4 cage complex is assembled from six 90° Pd(II) compounds [Pd(phen)(NO3)2, phen = 1,10-phenanthroline)] and four 120° trident ligands [2,4,6-tri(4-pyridyl)-1,3,5-triazine]. The size of the cage complex is verified by TEM image and electronic structure calculation. The cage complex can act as a host container that allows the encapsulation of suitable sized guest molecules, such as electroactive molecules (one is water-soluble, ferrocene methanol) and (the other is water-insoluble, ferrocene glycine ethyl ester). The host–guest complexes are characterized by NMR, IR, UV and electrochemical studies. Interestingly, under a 1.0 V electro-stimuli oxidation voltage, guest molecules encapsulated in the cage cavity are expelled upon oxidation (from neutral to monocations) respectively, which can evade from the cage cavity through controlling the reduction/oxidation state of small guest molecules.

Preparation of a Multicarbazole‐Based Nanocapsule Capable of Largely Modulating Guest Spectroscopic Properties in Water

A nanocapsule composed of multiple carbazole panels (ca. 12 panels) was quantitatively generated from bent carbazole-based amphiphiles in water. Unlike previously reported macrocycles and coordination cages bearing several carbazole panels, the resultant nanocapsule displays enhanced emissivity and improved electrochemical stability as compared with the monomeric amphiphile. The spectroscopic properties of substituted coumarin and boron-dipyrromethene dyes can be modulated upon encapsulation by the nanocapsule in water. In the cavity, a highly blue-shifted absorption band is observed from largely twisted coumarin dyes and two absorption bands are found from boron-dipyrromethene dimers stacked in an unusual L-shaped fashion. Moreover, the encapsulated dimers exhibit unique excimer-like emission.

Preparation of a Multicarbazole‐Based Nanocapsule Capable of Largely Modulating Guest Spectroscopic Properties in Water

AbstractA nanocapsule composed of multiple carbazole panels (ca. 12 panels) was quantitatively generated from bent carbazole‐based amphiphiles in water. Unlike previously reported macrocycles and coordination cages bearing several carbazole panels, the resultant nanocapsule displays enhanced emissivity and improved electrochemical stability as compared with the monomeric amphiphile. The spectroscopic properties of substituted coumarin and boron‐dipyrromethene dyes can be modulated upon encapsulation by the nanocapsule in water. In the cavity, a highly blue‐shifted absorption band is observed from largely twisted coumarin dyes and two absorption bands are found from boron‐dipyrromethene dimers stacked in an unusual L‐shaped fashion. Moreover, the encapsulated dimers exhibit unique excimer‐like emission.

Coordination-Driven Self-Assembly of Cyclometalated Iridium Squares Using Linear Aromatic Diisocyanides.

Here, we demonstrate facile [4 + 4] coordination-driven self-assembly of cyclometalated iridium(III) using linear aryldiisocyanide bridging ligands (BLs). A family of nine new [Ir(C^N)2(μ-BL)]44+ coordination cages is described, where C^N is the cyclometalating ligand-2-phenylpyridine (ppy), 2-phenylbenzothiazole (bt), or 1-phenylisoquinoline (piq)-and BL is the diisocyanide BL, with varying spacer lengths between the isocyanide binding sites. These supramolecular coordination compounds are prepared via a one-pot synthesis, with isolated yields of 40-83%. 1H NMR spectroscopy confirms the selective isolation of a single product, which is affirmed to be the M4L4 square by high-resolution mass spectrometry. Detailed photophysical studies were carried out to reveal the nature of the luminescent triplet states in these complexes. In most cases, phosphorescence arises from the [Ir(C^N)2]+ nodes, with the emission color determined by the cyclometalating ligand. However, in two cases, the lowest-energy triplet state resides on the aromatic core of the BL, and weak phosphorescence from that state is observed. This work shows that aromatic diisocyanide ligands enable coordination-driven assembly of inert iridium(III) nodes under mild conditions, producing supramolecular coordination complexes with desirable photophysical properties.

Synthesis and Characterization of an Isoreticular Family of Calixarene-Capped Porous Coordination Cages.

Functionalization of permanently porous coordination cages has been used to tune phase, surface area, stability, and solubility in this promising class of adsorbents. For many cages, however, these properties are intricately tied together, and installation of functional groups, for example, to increase solubility often leads to a decrease in surface area. Calixarene-capped cages offer the advantage in that they are cluster-terminated cages whose solid-state packing, and thus surface area, is typically governed by the nature of the capping ligand rather than the bridging ligand. In this work we investigate the influence of ligand functionalization on two series of isoreticular Ni(II)- and Co(II)-based calixarene-capped cages. The two types of materials described are represented as octahedral and rectangular prismatic coordination cages and can be synthesized in a modular manner, allowing for the substitution of dicarboxylate bridging ligands and the introduction of functional groups in specific locations on the cage. We ultimately show that highly soluble cages can be obtained while still having access to high surface areas for many of the isolated phases.