Cationic Ligands Research Articles

Hofmann Clathrates: A "Blue Box" Approach to Modulate Spin-Crossover Properties.

Hofmann coordination polymers (CPs) with cationic ligands provide an innovative strategy for recognizing π-electron-rich aromatic molecules - similar to the "little blue box". In this study, we demonstrate that hydroquinone molecules can be incorporated into these coordination polymers when redox-active bipyridinium derivatives are used as axial ligands. The insertion leads to a significant structural modification, resulting in a shift of the spin transition by 150 K and an approximate 23 % increase in volume, caused by the strong donor-acceptor π-π stacking interaction formed between the ligands and the guest molecule. These findings have been confirmed through temperature-dependent single crystal X-ray diffraction, magnetic measurements and optical reflectivity measurements.

Hofmann Clathrates: A “Blue Box” Approach to Modulate Spin‐Crossover Properties

AbstractHofmann coordination polymers (CPs) with cationic ligands provide an innovative strategy for recognizing π‐electron‐rich aromatic molecules – similar to the “little blue box”. In this study, we demonstrate that hydroquinone molecules can be incorporated into these coordination polymers when redox‐active bipyridinium derivatives are used as axial ligands. The insertion leads to a significant structural modification, resulting in a shift of the spin transition by 150 K and an approximate 23 % increase in volume, caused by the strong donor‐acceptor π‐π stacking interaction formed between the ligands and the guest molecule. These findings have been confirmed through temperature‐dependent single crystal X‐ray diffraction, magnetic measurements and optical reflectivity measurements.

Coordination complexes of iron(II) phthalocyanine with cationic, anionic and neutral ligands

A series of coordination complexes of iron(II) phthalocyanine (Fe[Formula: see text]Pc) with anionic, cationic and neutral ligands has been obtained in crystalline form. The salt of Fe[Formula: see text]Pc with MDABCO[Formula: see text] cations (MDABCO[Formula: see text][Fe[Formula: see text](Pc[Formula: see text]][Formula: see text]⋅(I[Formula: see text]⋅2TPC⋅2C6H4Cl2 (1) contains Fe[Formula: see text]Pc reduced to [Fe[Formula: see text](Pc[Formula: see text]][Formula: see text], and the Fe[Formula: see text] ion coordinates two cationic MDABCO[Formula: see text] ligands with the Fe-N(MDABCO[Formula: see text] bond length of 2.49–2.50 Å. The I[Formula: see text] anions are introduced into the phthalocyanine layers to compensate positive charge of the second MDABCO[Formula: see text] cation and form short hydrogen bonds with Pc. Preparation of dianionic salt of Fe[Formula: see text]Pc with the Bu3MeP[Formula: see text] cations by their reduction with sodium fluorenone ketyl yields a green solution characteristic of neutral Fe[Formula: see text]Pc. The solved structure shows deprotonation of the cations and the formation of Bu3PCH2 ylide which coordinates to Fe[Formula: see text]Pc in (Bu3PCH[Formula: see text][Fe[Formula: see text](Pc[Formula: see text]] (2). Two anionic acetylide (C[Formula: see text]CH[Formula: see text] or imidazole (Im[Formula: see text] ligands coordinate to Fe[Formula: see text]Pc by dissolving with cryptand and yielding {Cryptand(Na[Formula: see text]}2{(CCH[Formula: see text]Fe[Formula: see text](Pc[Formula: see text]}⋅2C6H4Cl2 (3) and {Cryptand(Na[Formula: see text]}2{(Im[Formula: see text]Fe[Formula: see text](Pc[Formula: see text]}⋅2C6H4Cl2 (4) complexes. In contrast to 1, complexes 2–4 are mainly neutral with weak charge transfer from ligands to Fe[Formula: see text], which is accompanied by the formation of Fe[Formula: see text] in 2 and 3.

Copper (II) halide compounds with cationic N-donor ligands: Design, synthesis, structure and magnetism

Copper (II) complexes of the cationic ligands 1-(4′-pyridyl)-pyridinium (L1) and 1-(4′-pyridyl)-pyridin-4-ol (L2) have been prepared and characterized by single crystal X-ray diffraction and variable temperature magnetic susceptibility measurements: [Cu(L1)2X2]X2 [where X = Cl (1), Br (2)], and [Cu(L2)2X2]X2 [where X = Cl (3), Br (4)]. The complexes are fundamentally square planar with L2X2 coordination planes and long, semi-coordinate bonds to the additional halide ions. All compounds crystallize in monoclinic systems with 1 and 2 in the P21/n space group and 3 and 4 in the P21/c space group. The crystal structures are stabilized by both non-classical (in the case of 1 and 2) and classical (3 and 4) hydrogen bonds. EPR data for 1–4 support a rhombohedral structure, in good agreement with the local geometry as seen in the crystal structures. Magnetic susceptibility measurements show the presence of very weak antiferromagnetic interactions. In addition, the syntheses and magnetic properties of two neutral complexes, [Cu(L3)2X2]·2H2O [L3 = 1-(4′-pyridino)-4-pyridone; X = Cl (5), Br (6)] are reported. Magnetic susceptibility data indicate the presence of moderate antiferromagnetic exchange interactions [J ∼ 28 K (5), 60 K (6)] which were well modeled by the S = 1/2 Heisenberg uniform chain model.

Giant chiral amplification of chiral 2D perovskites via dynamic crystal reconstruction.

Chiral hybrid perovskites show promise for advanced spin-resolved optoelectronics due to their excellent polarization-sensitive properties. However, chiral perovskites developed to date rely solely on the interaction between chiral organic ligand cations exhibiting point chirality and an inorganic framework, leading to a poorly ordered short-range chiral system. Here, we report a powerful method to overcome this limitation using dynamic long-range organization of chiral perovskites guided by the incorporation of chiral dopants, which induces strong interactions between chiral dopants and chiral cations. The additional interplay of chiral cations with chiral dopants reorganizes the morphological and crystallographic properties of chiral perovskites, notably enhancing the asymmetric behavior of chiral 2D perovskites by more than 10-fold, along with the highest dissymmetry factor of photocurrent (gPh) of ~1.16 reported to date. Our findings present a pioneering approach to efficiently amplify the chiroptical response in chiral perovskites, opening avenues for exploring their potential in cutting-edge optoelectronic applications.

Pressure-Induced High-Energy-Density BeN6 Materials: First-Principles study

Recently, the use of polymeric nitrogen in the search for high-energy–density materials (HEDMs) has attracted widespread attention. However, synthesizing polymeric nitrogen materials is quite challenging; for instance, the synthesis of cubic gauche nitrogen requires a high pressure of 110 GPa. Previous theoretical predictions and experiments have shown that adding alkaline earth metals as cationic ligands can stabilize polymeric nitrogen and reduce the synthesis pressure. Using the USPEX structural prediction code and first-principles calculations, this study predicted 2 new nitrogen salt with nitrogen contents up to 89.80 %, namely α-BeN6 and β-BeN6, with their unique nitrogen chain structures, have energy densities as high as 3.32 and 3.59 kJ/g, respectively. The exceptional explosive properties reveal these two BeN6 are potential HEDMs. In addition, α-BeN6 is a direct bandgap semiconductor.

Interactions Between Antimicrobial Peptides and Targets Responsible for their Nephrotoxic Action: Molecular Dynamics Simulations.

Polymyxin is the last line of defense against resistant forms of microorganisms, but it has significant nephrotoxicity. One of the directions in reducing the nephrotoxicity of polymyxin is to modify the charge of the molecule and accordingly, to change the topicity of the polymyxin derivative to the renal megalin. Such modification can lead to a decrease in the accumulation of polymyxin in the kidneys and reduce its toxicity while maintaining its antimicrobial properties. The study aimed to investigate the structural aspects of polymyxin nephrotoxicity at the atomic level to promote the more purposeful development of the polymyxin's derivatives with the lower nephrotoxic action. The molecular dynamics simulations of the complexes of polymyxin B and its derivative NAB7061 (that carries only three positive charges located within the macrocycle) with megalin were performed in program package YASARA structure with explicit water (TIP3P) and ions (0.9 % NaCl) in NPT ensemble using the AMRER03 force field. After 10 ns equilibration, each system was simulated at 298 K and pH 7.4 for a 25 ns production phase. Simulations were run twice for each molecular system. By molecular dynamics simulations, the possibility was shown for polymyxin to form a stable complex with two neighbor structural domains of megalin in accord with the universal mechanism of binding the cationic ligands by ligand-binding CR repeats of the LDLR-family receptors. It was reported that interactions of megalin with polymyxin were stronger than with its derivative having no positively charged groups outside the macrocycle. The structural prerequisites of these differences were revealed, explaining the less nephrotoxicity of such derivatives compared to polymyxin. Comparative molecular dynamics simulations of megalin interactions with polymyxin B and its derivative NAB7061, which carries no positive charges outside the macrocycle, revealed the possible structural prerequisites for the lower nephrotoxic action of such polymyxin derivatives. The weakening of polymyxins binding with megalin may become an effective preventive measure against polymyxin-induced nephrotoxicity.

Introducing Cationic Selenium-Containing Triazapentadiene Ligand Framework: Synthesis, Coordination Chemistry, and Antifungal Activity.

Positively charged ligands are scarce. Here, we report the synthesis of unprecedented cationic selenium-containing triazapentadiene ligand framework. The reaction between 2-pyridylselenyl reagents and NaN(CN)2 in a 2:1 ratio produces the sodium complexes featuring the cationic selenium-containing triazapentadiene (SeTAP) ligand. The sodium-to-metal transmetalation allows facile preparation of SeTAP metal complexes, as exemplified by the reactions with CuCl2, AgNO3, NaAuCl4, and FeCl3. Density functional theory calculations have been used to analyze and characterize the chalcogen bonding interactions observed in the solid state for these compounds. Moreover, antifungal properties of the SeTAP ligand and its metal complexes were screened for in vitro activity against several phytopathogenic fungi. Phoma eupyrena exhibited prominent sensitivity against the action of most of the tested compounds.

Grain size control on organo-clay complexation and REE fractionation in the Paleozoic strata of the Permian Basin (West Texas, U.S.A.)

As a major component of mudstone, clay minerals are known to conserve organic matter (OM) as well as a range of trace elements through the mechanisms of adsorption, encapsulation, and/or intercalation. The associations of the clay minerals on one hand and trace elements and OM on the other hand impact the diagenetic evolution of such rocks and is of substantial importance for their characterization and assessment. Subsurface core samples collected from Late Paleozoic mudstone within the Permian Basin of Texas were separated into four grain size fractions (>2 µm, 2 to 1 µm, 1 to 0.6 µm, and <0.6 µm) to determine the clay mineralogy, OM abundances, and rock geochemistry using a suite of diffraction, spectroscopic, and chemical analysis. All separates were largely consisted of illite-smectite (I-S), illite-tobelite-smectite (I-T-S), mica/illite and chlorite coupled with some minor quartz and feldspar. The smectite component of I-S was shown to increase with decreasing grain size fractions. Additionally, t he rise in the content of smectite interlayers correlated with an increase in the total organic carbon (TOC) content towards the finest grain size separates in all samples. This suggested that a significant portion of the TOC content resided in the fraction below 2 µm and that smectite interlayers promoted the preservation of OM. Rare earth elements (REE) concentrations were found to be the highest in the finest grain size separates and align with an increased content of smectite interlayers, denoting a plausible interaction between the two. Further on, REE and TOC concentrations display a significant positive correlation in all size fractions and increase with respect to smectite interlayer content. This three-component relation suggests the REE adsorption to illite-smectite was likely promoted by OM. Understanding the close relation between the clay minerals, OM, and trace element content is indicative of polyvalent cationic bridging, ligand exchange, and organo-metallic complexation, which eventually l eads to the enrichment of OM and fractionation of REE in mudstone.

Isomolar high-entropy engineering and Ac-coordination regulated nanocubic hydroxystannate for synergistic adsorption-photocatalytic acetaldehyde abatement under anoxic conditions

High-entropy materials have attracted increasing attention in many applications due to their unusual properties, yet little is known about the effects of cationic ratios and anionic ligands on their catalytic activity. Herein, a novel isomolar high-entropy and Ac-coordinated hydroxystannate nanocube (iHEOH-Ac) is fabricated using NaOH as precipitant and acetate anion as ligand in one step. The unique strategy simultaneously employing isomolar high-entropy engineering and Ac coordination in iHEOH-Ac synergistically facilitates the formation of oxygen vacancies and acid sites and significantly enhances optical absorption, charge separation and acetaldehyde activation, leading to the highest amount of ROS (•OH and •O2– and h+). The synergistic adsorption-photocatalytic performance of iHEOH-Ac in acetaldehyde abatement outperforms its net photocatalytic mode and other counterparts, with maximum removal ratio up to ∼ 100% under anoxic conditions and reversible deactivation of ∼ 10% over 360 min. This work not only sheds light on the enhancement mechanism on the acetaldehyde oxidation performance through isomolar high-entropy and Ac-coordinated strategy, but also successfully regulates the acetaldehyde oxidation pathways by the reaction mode and anionic coordination environment, providing a new route for the design of high-performance acetaldehyde oxidation photocatalysts under anoxic environments.

Cori Ester as the Ligand for Monovalent Cations.

Gerty T. and Carl F. Cori discovered, during research on the metabolism of sugars in organisms, the important role of the phosphate ester of a simple sugar. Glucose molecules are released from glycogen-the glucose stored in the liver-in the presence of phosphates and enter the blood as α-D-glucose-1-phosphate (Glc-1PH2). Currently, the crystal structure of three phosphates, Glc-1PNa2·3.5·H2O, Glc-1PK2·2H2O, and Glc-1PHK, is known. Research has shown that reactions of Glc-1PH2 with carbonates produce new complexes with ammonium ions [Glc-1P(NH4)2·3H2O] and mixed complexes: potassium-sodium and ammonium-sodium [Glc-1P(X)1.5Na0.5·4H2O; X = K or NH4]. The crystallization of dicationic complexes has been carried out in aqueous systems containing equimolar amounts of cations (1:1; X-Na). It was found that the first fractions of crystalline complexes always had cations in the ratio 3/2:1/2. The second batch of crystals obtained from the remaining mother liquid consisted either of the previously studied Na+, K+ or NH4+ complexes, or it was a new sodium hydrate-Glc-1PNa2·5·H2O. The isolated ammonium-potassium complex shows an isomorphic cation substitution and a completely unique composition: Glc-1PH(NH4)xK1-x (x = 0.67). The Glc-1P2- ligand has chelating fragments and/or bridging atoms, and complexes containing one type of cation show different modes of coordinating oxygen atoms with cations. However, in the case of the potassium-sodium and ammonium-sodium structures, high structural similarities are observed. The 1D and 2D NMR spectra showed that the conformation of Glc-1P2- is rigid in solution as in the solid state, where only rotations of the phosphate group around the C-O-P bonds are observed.

Ultrastable Copper Iodide Hybrid with Intrinsic Greenish White-Light Emission by Incorporating an Anionic Inorganic Functional Unit into an Extended Structure.

Incorporating a functional unit into the multidimensional coordination polymer skeleton is an efficient way to improve the stability of materials and expand their application. In this paper, anionic copper iodide inorganic functional modules are incorporated into one-dimensional extended chains by using a unique bidentate cationic organic ligand. Benefiting from the ionic extended structure, the resulting hybrid possesses a remarkable stability with a decomposition temperature as high as 300 °C. Meanwhile, the hybrid material exhibits intrinsic greenish white-light emission with a high photoluminescent quantum yield of 70%. The emission was investigated by temperature-dependent emission spectra, which proved to be the result of the synergistic effect of two energy states. The novel synthetic strategy provides an efficient route for the development of functional organic metal halides.

Transcriptional profiling of primary human-skin derived mast cell activation by various MRGPRX2 agonists and inhibition with EVO756

Abstract Mas-related G-protein coupled receptor X2 (MRGPRX2) is a GPCR expressed predominantly by mast cells and has been implicated to play an important role in diseases such as chronic spontaneous urticaria, atopic dermatitis, and asthma. Cationic ligands, either endogenous or exogenous, can activate the receptor and induce IgE-independent mast cell activation, resulting in allergic responses and non-histaminergic itch. We have previously shown that EVO756, a novel small molecule antagonist of MRGPRX2, demonstrates potent, concentration dependent inhibition of MRGPRX2 mediated activation of transfected CHO-cells, ROSA and LAD2 mast cell lines, and primary human skin-derived mast cells. Furthermore, EVO756 does not affect mast cell viability. Here, we describe, for the first time, the transcriptional landscape of primary human skin-derived mast cells cultured in the presence of several MRGPRX2 agonists and analyze how the mast cell phenotype is altered in response to MRGPRX2 inhibition by EVO756.

Enhanced antibacterial activity of polyphenol-bound microtopography by synergistic chemical and micro/nanomechanical effects

Initial microbial attachment on surfaces is the first step in bacteria contamination and direct intervention in the early adhesion stage by constructing an antibacterial coating is an effective strategy to prevent the attachment and proliferation of bacteria. Herein, a storable polyphenol-based coating is designed and fabricated by self-assembling the cationic template and ionic ligand. The materials containing microparticles with sticky properties inherited from tannic can be deposited on various surfaces by a simple redispersion-immersion process. The functional ligands on the outer layer of the coating can kill bacteria by combining chemical damages produced by tannic as well as mechanical disruption caused by the micro-nano topography as reflected by the elevated Young's modulus and differentiated stiffness of the bacterial membrane. The results reveal a simple method to prepare polyphenol-based antibacterial coatings and enrich our understanding of the combined use of chemical and mechanical interventions to enhance the antibacterial activity.

External Trigger Free Charge Switchable Cationic Ligands in the Design of Safe and Effective Universal Heparin Antidote.

Thrombosis, the formation of blood clots within a blood vessel, can lead to severe complications including pulmonary embolism, cardiac arrest, and stroke. The most widely administered class of anticoagulants is heparin-based anticoagulants such as unfractionated heparin, low-molecular weight heparins (LMWHs), and fondaparinux. Protamine is the only FDA-approved heparin antidote. Protamine has limited efficacy neutralizing LMWHs and no reversal activity against fondaparinux. The use of protamine can lead to complications, including excessive bleeding, hypotension, and hypersensitivity, and has narrow therapeutic window. In this work, a new concept in the design of a universal heparin antidote: switchable protonation of cationic ligands, is presented. A library of macromolecular polyanion inhibitors (MPIs) is synthesized and screened to identify molecules that can neutralize all heparins with high selectivity and reduced toxicity. MPIs are developed by assembling cationic binding groups possessing switchable protonation states onto a polymer scaffold. By strategically selecting the identity and modulating the density of cationic binding groups on the polymer scaffold, a superior universal heparin reversal agent is developed with improved heparin-binding activity and increased hemocompatibility profiles leading to minimal effect on hemostasis. The activity of this heparin antidote is demonstrated using in vitro and in vivo studies.

Colloidal Aziridinium Lead Bromide Quantum Dots.

The compositional engineering of lead-halide perovskite nanocrystals (NCs) via the A-site cation represents a lever to fine-tune their structural and electronic properties. However, the presently available chemical space remains minimal since, thus far, only three A-site cations have been reported to favor the formation of stable lead-halide perovskite NCs, i.e., Cs+, formamidinium (FA), and methylammonium (MA). Inspired by recent reports on bulk single crystals with aziridinium (AZ) as the A-site cation, we present a facile colloidal synthesis of AZPbBr3 NCs with a narrow size distribution and size tunability down to 4 nm, producing quantum dots (QDs) in the regime of strong quantum confinement. NMR and Raman spectroscopies confirm the stabilization of the AZ cations in the locally distorted cubic structure. AZPbBr3 QDs exhibit bright photoluminescence with quantum efficiencies of up to 80%. Stabilized with cationic and zwitterionic capping ligands, single AZPbBr3 QDs exhibit stable single-photon emission, which is another essential attribute of QDs. In particular, didodecyldimethylammonium bromide and 2-octyldodecyl-phosphoethanolamine ligands afford AZPbBr3 QDs with high spectral stability at both room and cryogenic temperatures, reduced blinking with a characteristic ON fraction larger than 85%, and high single-photon purity (g(2)(0) = 0.1), all comparable to the best-reported values for MAPbBr3 and FAPbBr3 QDs of the same size.

Thermotropic Structure Phase Transitions and Two Types of Thermochromic Behaviors in a Bromoargentate Cluster [Pr-dabco]2Ag4Br6.

Organic-inorganic silver halide hybrids show abundant phase transitions and thermochromism. However, it is very rare that silver halides exhibit thermochromism related to thermotropic structure phase transition. Herein, a bromoargentate hybrid, [Pr-dabco]2Ag4Br6 (1) (Pr-dabco+ = 1-propyl-1,4-diazabicyclo-[2.2.2]octan-1-ium), with tetranuclear [Ag4Br6]2- clusters was prepared and characterized by microanalysis, ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, and thermogravimetric (TG) and differential scanning calorimetry (DSC) techniques. Interestingly, 1 undergoes an irreversible structure phase transition at ∼436 K in the first heating process, which is accompanied by an abrupt color change from colorless to yellow; however, a reversible color change between pale yellow and yellow is observed in the next heating-cooling cycles. Notably, DSC measurement revealed that a reversible phase transition is associated with the change in color between pale yellow and yellow, while the powder X-ray diffraction (PXRD) patterns corresponding to pale yellow and yellow phases are quite similar to each other. These observations demonstrate that thermochromism in the next heating-cooling runs is associated with a reversible structure phase transition, which perhaps concerns the disorder-order transformation of alkyl chains in the cationic ligand [Pr-dabco]+, and relevant to the anharmonic fluctuations of the Ag-Br and Ag-N bonds, a strong electron-phonon coupling effect is seen within the bromoargentate cluster.

Cationic ligands - from monodentate to pincer systems.

For a long time, the small group of cationic ligands stood out as obscure systems within the general landscape of coordinative chemistry. However, this situation has started to change rapidly during the last decade, with more and more examples of metal-coordinated cationic species being reported. The growing interest in these systems is not only of purely academic nature, but also driven by accumulating evidence of their high catalytic utility. Overcoming the inherently poor coordinating ability of cationic species often required additional structural stabilization. In numerous cases this was realized by functionalizing them with a pair of chelating side-arms, effectively constructing a pincer-type scaffold. This comprehensive review aims to encompass all cationic ligands possessing such pincer architecture reported to date. Herein every cationic species that has ever been embedded in a pincer framework is described in terms of its electronic structure, followed by an in-depth discussion of its donor/acceptor properties, based on computational studies (DFT) and available experimental data (IR, NMR or CV). We then elaborate on how the positive charge of these ligands affects the spectroscopic and redox properties, as well as the reactivity, of their complexes, compared to those of the structurally related neutral ligands. Among other systems discussed, this review also surveys our own contribution to this field, namely, the introduction of sulfonium-based pincer ligands and their complexes, recently reported by our group.

Geometries and stabilities of chromium doped nitrogen clusters: mass spectrometry and density functional theory studies.

Metal-doped nitrogen clusters serve as effective models for elucidating the geometries and electronic properties of nitrogen-rich compounds at the molecular scale. Herein, we have conducted a systematic study of VIB-group metal chromium (Cr) doped nitrogen clusters through a combination of mass spectrometry techniques and density functional theory (DFT) calculations. The laser ablation is employed to generate CrNn+ clusters. The results reveal that CrN8+ cluster exhibits the highest signal intensity in mass spectrometry. The photodissociation experiments with 266 nm photons confirm that the chromium heteroazide clusters are composed of chromium ions and N2 molecules. Further structural searches and electronic structure calculations indicate that the cationic CrN8+ cluster possesses an X shaped geometry with D2 symmetry and exhibits robust stability. Molecular orbital and chemical bonding analyses demonstrate the existence of strong interactions between Cr+ cation and N2 ligands. The present findings enrich the geometries of metal doped nitrogen clusters and provide valuable guidance for the rational design and synthesis of novel transition metal nitrides.

A novel energetic pyridine-2-carbohydrazide copper perchlorate complex: synthesis, cationic ligand structure and properties

The pyridine-2-carbohydrazide copper perchlorate complex was synthesized, and it possessed high thermal stabilitiy and moderate sensitivity which was sensitive to laser and could detonate RDX.