Cyclic Ligands Research Articles

Linkage of the Dinuclear Gold(I) Complex Luminescence and Origin of Endocyclic Amino Group of Cyclic P2N2-Bridging Ligands.

Gold(I) complexes of LAu2Cl2 composition based on P2N2 ligands, namely 1,5-diaza-3,7-diphosphacyclooctanes, containing ethylpyridyl substituents at the phosphorus atoms and sp2- or sp3-hybridized endocyclic nitrogen atoms were synthesized. The SCXRD analysis indicated the strong impact of the geometry of the nitrogen atom on the structure and conformational flexibility of the complexes. The N-aryl substituted ligand with the planar endocyclic nitrogen atom provides higher flexibility of the complex and an ability to bind the solvent molecules in the "host-guest" mode, whereas that kind of behavior is forbidden for the complex with an N-alkyl substituted ligand with a pyramidal nitrogen atom. The substituents at nitrogen atoms also control the origin of the emission, which is phosphorescence for the N-aryl substituted complex and fluorescence for the N-alkylaryl substituted complex. The phosphorescent gold(I) complex displays high cytotoxicity without selectivity toward the m-HeLa and normal cells, but the core-shell nanoparticles formed on the base of the complex demonstrate reduced cytotoxicity. The luminescence of the NPs allows tracking the complexes in the cell samples.

Cu(I)-thioether coordination complexes based on a chiral cyclic β-amino acid ligand

Coordination complexes, particularly metalloproteins, highlight the significance of metal-sulfur bonds in biological processes. Their unique attributes inspire efforts to synthetically reproduce these intricate metal-sulfur motifs. Here, we investigate the synthesis and characterization of copper(I)-thioether coordination complexes derived from copper(I) halides and the chiral cyclic β-amino acid trans-4-aminotetrahydrothiophene-3-carboxylic acid (ATTC), which present distinctive structural properties and ligand-to-metal ratios. By incorporating ATTC as the ligand, we generated complexes that feature a unique chiral conformation and the capacity for hydrogen bonding, facilitating the formation of distinct geometric structures. Through spectroscopic analyses and density functional theory (DFT) calculations, we studied the complexes’ optical properties, including their emission bands and variable second-harmonic generation (SHG) efficiencies, which vary based on the halide used. Our findings underscore the potential of the ATTC ligand in creating unusual coordination complexes and pave the way for further investigations into their potential applications, particularly within materials science.

Ligand presentation inside protein crystal nanopores: Tunable interfacial adhesion noncovalently modulates cell attachment

Protein crystals with sufficiently large solvent pores can non-covalently adsorb polymers in the pores. In principle, if these polymers contain cell adhesion ligands, the polymer-laden crystals could present ligands to cells with tunable adhesion strength. Moreover, porous protein crystals can store an internal ligand reservoir, so that the surface can be replenished. In this study, we demonstrate that poly (ethylene glycol) terminated with a cyclic cell adhesion ligand peptide (PEG-RGD) can be loaded into porous protein crystals by diffusion. Through atomic force microscopy (AFM), force-distance correlations of the mechanical interactions between activated AFM tips and protein crystals were precisely measured. The activation of AFM tips allows the tips to interact with PEG-RGD that was pre-loaded in the protein crystal nanopores, mimicking how a cell might attach to and pull on the ligand through integrin receptors. The AFM experiments also simultaneously reveal the detailed morphology of the buffer-immersed nanoporous protein crystal surface. We also show that porous protein crystals (without and with loaded PEG-RGD) serve as suitable substrates for attachment and spreading of adipose-derived stem cells. This strategy can be used to design surfaces that non-covalently present multiple different ligands to cells with tunable adhesive strength for each ligand, and with an internal reservoir to replenish the precisely defined crystalline surface.

Molecular design and systematic optimization of a halogen-bonding system between the asthma interleukin-5 receptor and its cyclic peptide ligand.

Human interleukin-5 (IL-5) functions as an important pro-inflammatory factor by binding to its specific receptor, IL-5Rα, which has been implicated in the pathogenesis of asthma. Previously, a disulfide-bonded cyclic peptide AF17121 obtained from random library screening and sequence variation was found to competitively disrupt the cognate IL-5Rα/IL-5 interaction with moderate potency. In this study, the crystal complex of IL-5Rα with AF17121 was investigated at structural and energetic levels. It is revealed that the side-chain indole moiety of the AF17121 Trp5 residue is a potential site for a stem putative halogen bond (X-bond) with IL-5Rα, which is just located within the key 3 EXXR6 motif region recognized specifically by IL-5Rα. We systematically examined four halogen substitution types at five positions of the indole moiety; QM/MM calculations theoretically unraveled that only halogenations at 5 and 6 positions can form effective X-bonds with the side-chain hydroxyl oxygen of the IL-5Rα Thr21 residue and the backbone carbonyl oxygen of Ala66 residue, respectively. Binding assays observed that I-substitution at the 5 position and Br-substitution at the 6 position can result in two potent halogenated peptides, [5I]AF17121 and [6Br]AF17121, which are improved by 1.6-fold and 3.5-fold relative to the native AF17121, respectively. 5I/6Br-double substitution, resulting in [5I/6Br]AF17121, can further enhance the peptide affinity by 7.5-fold. Structural analysis revealed that the X-bond stemming from 6Br-substitution is also involved in an orthogonal interaction system with a H-bond; they share a common backbone carbonyl oxygen acceptor of IL-5Rα Ala66 residue and exhibit a significant synergistic effect between them.

Urotensin II Receptor Modulation with 1,3,4-Benzotriazepin-2-one Tetrapeptide Mimics.

Urotensin II receptor (UT) modulators that differentiate the effects of the endogenous cyclic peptide ligands urotensin II (UII) and urotensin II-related peptide (URP) offer potential for dissecting their respective biological roles in disease etiology. Selective modulators of hUII and URP activities were obtained using 1,3,4-benzotriazepin-2-one mimics of a purported bioactive γ-turn conformation about the Bip-Lys-Tyr tripeptide sequence of urocontrin ([Bip4]URP). Considering an active β-turn conformer about the shared Phe-Trp-Lys-Tyr sequence of UII and URP, 8-substituted 1,3,4-benzotriazepin-2-ones were designed to mimic the Phe-Bip-Lys-Tyr tetrapeptide sequence of urocontrin, synthesized, and examined for biological activity. Subtle 5- and 8-position modifications resulted in biased signaling and selective modulation of hUII- or URP-induced vasoconstriction. For example, p-hydroxyphenethyl analogs 17b-d were strong Gα13 and βarr1 activators devoid of Gαq-mediated signaling. Tertiary amides 15d and 17d negatively modulated hUII-induced vasoconstriction without affecting URP-mediated responses. Benzotriazepinone carboxamides proved to be exceptional tools for elucidating the pharmacological complexity of UT.

Potentiating the Systemic Immunity by Bacteria‐Delivered Sting Activation in a Tumor Microenvironment

AbstractStimulator of interferon genes (STING) connects the innate immunity to potent adaptive immunity via multiple pathways, which play a critical role in cancer treatment. Clinical application of STING agonists is mainly restrained due to the metabolic instability caused by intrinsic cyclic dinucleotide ligands. Previously, an orally available non‐nucleotide human STING agonist, MSA‐2 is presented, and to further improve its therapeutic efficacy, this work leverages the nonpathogenic Escherichia coli Nissle 1917 for tumor‐targeted delivery of the STING agonist by coating biocompatible polydopamine on the bacterial surface, termed as PDMN. The engineered bacterial delivery platform holds potential in elevating levels of type I interferon (IFN) along with proinflammatory cytokines and inducing maturation on dendritic cells. Intravenous administration of PDMN with laser irradiation to the tumor region promotes IFN‐β expression in a tumor microenvironment and mounts both the innate and adaptive immune responses, leading to profound regressions of established melanoma and hepatocellular carcinoma in mice. By synergized with anti‐PD‐1 therapy, a substantial long‐lived protective immunity is generated, capable of preventing distant tumor metastases. Hence, this study identifies a STING‐amplified biotherapy to shape the cell‐mediated antitumor immunity, serving as a potential personalized cancer vaccine with enhanced biosafety and immune activation profile for diverse applications.

Using reactivity predictors for enhancing the electrocatalytic activity of MN4 molecular catalysts for the oxygen reduction reaction: The role of the N-pyridinium functional group in the porphyrazine-derivative ligands

Using reactivity predictors to enhance or control the electrocatalytic activity of materials is a fascinating concept. This is especially true for the development of alternative platinum metal group-free materials as it facilitates the rational design of active catalytic materials for the oxygen reduction reaction (ORR). In previous work, we have found that the peripheral and non-peripheral electron-withdrawing effects and the electron-pull effect from axial extraplanar ligand in iron-phthalocyanine (FePc) are key factors in improving the binding energy between the active Fe site and O2 resulting in an increase of the electrocatalytic activity of FePcs for the ORR. In this work, we have utilized fundamental principles of electrocatalysis and DFT calculations to design and synthesize FeN4 molecular catalysts to increase their catalytic performance for the ORR through the "pull" effect. To achieve this, by chemical synthesis, we have incorporated pyridinium functional groups (N+py) in peripheral and non-peripheral positions into the porphyrazine cyclic ligands. In this fashion we obtain the porphyrazinium molecular catalysts, [Fe(II)2,3-(TMe)TPyPz]4+ and [Fe(II)3,4-(TMe)TPyPz]4+. Because these new compounds are not commercially available and, to the best of our knowledge, they have not been tested for ORR. In order to determine their effectiveness, we have compared porphyrazinium with neutral analog porphyrazine compounds (Fe(II)TPyPz) and perfluorinated and perchlorinated iron phthalocyanines, which are currently the best molecular catalysts for ORR. The electrocatalytic activity was determined for each molecular catalyst deposited on the edge plane of a graphite electrode (EPG) surface in an alkaline medium. Only for the purpose of comparison we include two Fe porphyrins studied previously, which show low activity for ORR. Although the DFT theoretical analysis of porphyrazinium complexes suggests a high activity for these catalysts, our experimental findings revealed the opposite trend. Therefore, this finding makes us reconsider the interfacial effects, such as the counter-ions effects on N+py that could influence the electron-pull effect, opening new insights for designing molecular catalysts considering interface engineering. Moreover we report for the first time, the reactivity linear relationship between the metal-centered redox potential gap (E°Fe(III)/(II) – E°Fe(II)/(I))) with the electrocatalytic activity for ORR for all catalysts studied, emerging this potential gap as a possible and promising new reactivity descriptor for ORR in MN4 catalyst.

The versatility of 1,4,8,11-tetraazacyclotetradecane (cyclam) in the formation of compounds of Co2+, Ni2+, Cu2+, and Zn2+ with metal ions in and out of the cyclic ligand ring

Abstract Herein we report the results of preparing metal compounds (where the metal ions are Co2+, Ni2+, Cu2+, Zn2+) with the cyclic ligand 1,4,8,11-tetraazacyclotetradecane [cyclam] under a variety of conditions of metal-ligand ratios and solvent media. In all cases, we used metal Cl2·nH2O salts (except for anhydrous CoCl2), as specified. Outcome: we isolated species with a four-coordinate metal in the N4 cavity of the ligand alone, and also with either one or two additional axial ligands. Those axial ligands can be (a) a single chloride, leading to penta-coordinated moncationic products; (b) two chlorides, leading to octahedral-neutral compounds; (c) two waters, giving rise to hexa-coordinated [(cyclam)metal(H2O)2]2+ species. Finally, in the case of HCl added to the reaction medium, the cyclam can be di-protonated and appears as [(cyclam)H2]2+ in the crystals. With such a variety of products, it is not surprising that since the metal coordination numbers vary, the cyclam ligand stereochemistries are thereby affected. Interestingly, the [(cyclam)metal] species are invariably hydrogen-bonded to one another in infinite strings of two kinds: (1) those for which the crystal’s Z′ = 1 have single strings; (2) when Z′ = 2, there is a pair of homogeneous strings attached to one another by a variety of hydrogen-bonding linkages. Finally, we observed an interesting pair of hydroxonium cations: the first is hydoxonium cations in a pleated 2-D sheet consisting of fused pentagons located between sheets of [(cyclam)metal] moieties; the second one is an infinite string of composition {(H3O+)-(H2O)-(H3O+)-(H2O)-(H3O+)-(H2O)-(H3O+)}∞.

Comparative study of interaction energies between αIIbβ3 integrin and the peptidic, peptidomimetic and non-peptidic ligands by quantum mechanics FMO-PIEDA calculations

Integrins belong to a family of cell adhesion receptors. To better understand an adhesion mechanism of integrins, fragmented molecular orbital (FMO) method with pair interaction energy decomposition analysis (PIEDA) was applied for integrin:ligand complexes. Interaction energies were evaluated between the amino acid residues including Mg2+ and Ca2+ ions at ligand-binding site of αIIbβ3 integrin and two peptide chains with the Ala-Gly-Asp (AGD)- and the Arg-Gly-Asp (RGD)-binding motifs, a cyclic peptide (eptifibatide), peptidomimetic ligands (tirofiban and L-739758) and poly(l-lactic acid) chain (PLA). The results indicate that Mg2+ and Ca2+ ions together with Asp224A, Asn215B, Asp159A and Lys125B of αIIbβ3 are the most important residues for a binding of the peptidic ligands while for the peptidomimetic ligands and PLA, interactions with Ca2+ ions are less significant than those with amino acid residues of αIIbβ3. For all complexes, a dominant part of interaction energy comes from electrostatic interactions. New developed antagonists of αIIbβ3 should mimic not only the interactions of the RGD motif but also the interactions of the backbone of a longer peptidic sequence (RGDV or AGDV) with the focus on the interactions of the antagonists with the ADMIDAS Ca2+ ion. An interaction pattern predicted for PLA was compared with the native peptidic ligands.

Structural and Magnetic Properties of the {Cr(pybd)3[Cu(cyclen)]2}(BF4)4 Heteronuclear Complex

Heterotopic ligands containing chemically different binding centers are appealing candidates for obtaining heteronuclear metal complexes. By exploiting this strategy, it is possible to introduce different paramagnetic centers characterized by specific anisotropic magnetic properties that make them distinguishable when weakly magnetically coupled. This molecular approach has great potential to yield multi-spin adducts capable of mimicking logical architectures necessary for quantum information processing (QIP), i.e., quantum logic gates. A possible route for including a single-ion magnetic center within a finite-sized heterometallic compound uses the asymmetric (1-pyridyl)-butane-1,3-dione (pybd) ligand reported in the literature for obtaining Cr3+−Cu2+ metallo-cages. To avoid the formation of cages, we adopted the cyclen (1,4,7,10-tetraazacyclododecane) ligand as a “capping” agent for the Cu2+ ions. We report here the structural and magnetic characterization of the unprecedented adduct {Cr(pybd)3[Cu(cyclen)]2}(BF4)4, whose structure is characterized by a central Cr3+ ion in a distorted octahedral coordination environment and two peripheral Cu2+ ions with square-pyramidal coordination geometries. As highlighted by Continuous Wave Electron Paramagnetic Resonance (EPR) spectroscopy and Direct Current (DC) magnetometry measurements, this adduct shows negligible intramolecular magnetic couplings, and it maintains the characteristic EPR signals of Cr3+ and Cu2+ moieties when diluted in frozen solutions.

A cyclic azapeptide ligand of the scavenger receptor CD36/SR-B2 reduces the atherosclerotic lesion progression and enhances plaque stability in apolipoprotein E-deficient mice.

Atherosclerosis is a chronic inflammatory disease of the arterial walls that develops at predisposed sites. As a major risk factor for adverse cardiovascular pathology, atherosclerosis can progress to myocardial infarction and stroke, due to the rupture of unstable atherosclerotic lesions. Macrophage uptake of modified lipoproteins and metabolic dysfunction contributes significantly to the initiation and development of atherosclerotic lesions. The cluster of differentiation 36 receptor [CD36 (SR-B2)] plays a key role in atherosclerotic lesion progression and acts as an efferocytic molecule in the resolution of advanced plaque. In previous studies, linear azapeptide CD36 ligands were shown to exhibit anti-atherosclerotic properties. In the present study, a novel potent and selective macrocyclic azapeptide CD36 ligand, MPE-298, has proven effective in protecting against atherosclerosis progression. Features of greater plaque stability were observed after 8 weeks of daily injections with the cyclic azapeptide in apolipoprotein E-deficient mice fed a high-fat high-cholesterol diet.

Effect of Acidic Strength of Surface Ligands on the Carrier Relaxation Dynamics of Hybrid Perovskite Nanocrystals.

Perovskite nanocrystals (PeNCs) are known for their use in numerous optoelectronic applications. Surface ligands are critical for passivating surface defects to enhance the charge transport and photoluminescence quantum yields of the PeNCs. Herein, we investigated the dual functional abilities of bulky cyclic organic ammonium cations as surface-passivating agents and charge scavengers to overcome the lability and insulating nature of conventional long-chain type oleyl amine and oleic acid ligands. Here, red-emitting hybrid PeNCs of the composition CsxFA(1-x)PbBryI(3-y) are chosen as the standard (Std) sample, where cyclohexylammonium (CHA), phenylethylammonium (PEA) and (trifuluoromethyl)benzylamonium (TFB) cations were chosen as the bifunctional surface-passivating ligands. Photoluminescence decay dynamics showed that the chosen cyclic ligands could successfully eliminate the shallow defect-mediated decay process. Further, femtosecond transient absorption spectral (TAS) studies uncovered the rapidly decaying non-radiative pathways; i.e., charge extraction (trapping) by the surface ligands. The charge extraction rates of the bulky cyclic organic ammonium cations were shown to depend on their acid dissociation constant (pKa) values and actinic excitation energies. Excitation wavelength-dependent TAS studies indicate that the exciton trapping rate is slower than the carrier trapping rate of these surface ligands.

Selective Oxidation of Alkylarene in H2O Catalyzed by the Polyoxometalate Supported Chromium Catalyst

AbstractThe selective oxidation of alkylarene is a quite straightforward and appealing way for production of aromatic aldehydes, ketones and aromatic acid derivatives. We synthesized Cr(III) catalyst, (NH4)3[CrMo6O18(OH)6], with reasonable activity towards selective oxidation of alkylarenes under mild conditions. The catalyst is supported by a central chromium mononucleus and a cyclic inorganic ligand composed of six MoVIO6 octahedra, avoiding the disadvantages of expensive and non‐recyclable organic ligand. It is efficient, green and can be recycled at least six times with high activity. At the same time, a wide range of substituted alkylarenes were found to be compatible, providing the corresponding carbonyl compounds in moderate‐to‐high yield.

New Heterocyclic Organo-Chalcogenide Compounds: Synthesis, Physicochemical Characterization, and Evaluation of Anticancer Activity against Breast Cancer Cells

This work aimed to synthesize, characterize and evaluate the thermal stability of new sulfur and selenium organochalcogenide derivatives and to test the cytotoxic activity against breast adenocarcinoma cell line (MCF-7) through conducting MTT assay and AO/EB dual staining-technique. Two series of ten organo-chalcogen compounds: 4-(substituted)phenylthiomorpholine-3,5-dione and 4-(substituted)phenylselenomorpholine-3,5-dione were prepared by the reaction of Na2S·3H2O and NaHSe with N-(substituted)phenyl-2-chloro-N-(2-chloroacetyl)acetamide, respectively, under nitrogen atmosphere to give the corresponding cyclic chalcogenide ligands. All new compounds were characterized by melting point, FTIR, elemental analysis, UV-Visible, 1H-NMR and 13C-NMR. Meanwhile, TG/DTA analysis of some of these ligands was conducted to evaluate the thermal stability, kinetic, and characteristic thermodynamic parameters. Absorption spectroscopy was used to investigate these compounds with human DNA. The experimental results investigated a hypochromic effect via intercalation binding mode. The role of the prepared ligands in breast cell lines has been investigated by conducting MTT assay via spectroscopic techniques on HBL100 and MCF-7, normal and cancer breast cell lines, respectively. Cell death was seen after AO/EB dye staining method employing the fluorescence microscopy technique. The results revealed that these compounds possess cytotoxic activity on the MCF-7 and HBL-100 cell lines at a fixed concentration.

Molecular engineering of cyclic azobenzene-peptide hybrid ligands for the purification of human blood Factor VIII via photo-affinity chromatography.

The use of benign stimuli to control the binding and release of labile biologics for their isolation from complex feedstocks is a key goal of modern biopharmaceutical technology. This study introduces cyclic azobenzene-peptide (CAP) hybrid ligands for the rapid and discrete photo-responsive capture and release of blood coagulation Factor VIII (FVIII). A predictive method - based on amino acid sequence and molecular architecture of CAPs - was developed to correlate the conformation of cis/trans CAP photo-isomers to FVIII binding and release. The combined in silico and in vitro analysis of FVIII:peptide interactions guided the design of a rational approach to optimize isomerization kinetics and biorecognition of CAPs. A photoaffinity adsorbent, prepared by conjugating selected CAP G-cycloAZOB[Lys-YYKHLYN-Lys]-G on translucent chromatographic beads, featured high binding capacity (> 6 mg of FVIII per mL of resin) and rapid photo-isomerization kinetics (τ < 30s) when exposed to 420-450 nm light at the intensity of 0.1 W·cm-2. The adsorbent purified FVIII from a recombinant harvest using a single mobile phase, affording high product yield (>90%), purity (>95%), and blood clotting activity. The CAPs introduced in this report demonstrate a novel route integrating gentle operational conditions in a rapid and efficient bioprocess for the purification of life-saving biotherapeutics.

Comparison of Photophysical Properties of Lanthanide(III) Complexes of DTTA- or DO3A-Appended Aryl-2,2'-Bipyridines.

New Tb(III) and Eu(III) complexes based on aryl-2,2'-bipyridine ligands with a cyclic DO3A chelating unit appended in the alpha position of the bipyridine core were synthesized. The photophysical properties of these complexes were compared with those of complexes of ligands with identical aryl-2,2'-bipyridine chromophores, but with an acyclic DTTA residue as an additional chelating site in the alpha position of the bipyridine core. The nature of the polyaminocarboxylic acid fragments was found to have a significant influence on the luminescence. For some of the Eu(III) complexes, upon the transition from acyclic DTTA- to the cyclic DO3A-appended ligands, a noticeable increase in the intensity of Eu(III) luminescence was observed, with an increase in the quantum yield of up to 2.55 times. In contrast, for most of the Tb(III) complexes, a similar transition resulted in a noticeable decrease in the luminescence intensity of the Tb(III) cation.

Asymmetric transfer hydrogenation of ketones catalyzed by chiral macrocyclic cobalt(II) complexes

Using easily available CoBr2 and chiral cyclic PxNy-type ligands as starting materials, novel chiral cyclic cobalt(II) complexes could be conveniently prepared. Furthermore, we obtained the single crystals suitable for X-ray diffraction to confirm the structures of these cobalt(II) complexes. The asymmetric transfer hydrogenation (ATH) of ketones catalyzed by these well-designed cobalt(II) complexes was investigated. Among them, cobalt(II) complex containing chiral macrocyclic iminophosphine ligand CyP2N4 exhibited high catalytic activity and enantioselectivity (up to 99% ee). Density functional theory (DFT) calculations suggested that cobalt(II) complex (R,R,R',R')-CyP2N4-Co(II) (C1) is easier to form metal hydride, which is the key intermediate during the enantioselective transfer hydrogenation reaction. Study results also revealed that the unique macrocyclic structure of complex C1 could form a special microenvironment around cobalt ion. Therefrom the substrate coordinated with the central metal along this specific reaction channel during the asymmetric catalytic reaction, resulting high enantioselectivity.

Halogen-Bonding-Mediated Radical Reactions: The Unexpected Behavior of Piperazine-Based Dithiooxamide Ligands in the Presence of Diiodine.

N,N'-Dialkylpiperazine-2,3-dithiones (R2pipdt) were recognized as a class of hexa-atomic cyclic dithiooxamide ligands with peculiar charge-transfer donor properties toward soft electron-acceptors such as noble metal cations and diiodine. The latter interaction is nowadays better described as halogen bonding. In the reaction with diiodine, R2pipdt unexpectedly provides the corresponding triiodide salts, differently from the other dithiooxamides, which instead typically achieve ligand·nI2 halogen-bonded adducts. In this paper, we report a combined experimental and theoretical study that allows elucidation of the nature of the cited products and the reasons behind the unpredictable behavior of these ligands. Specifically, low-temperature single-crystal X-ray diffraction measurements on a series of synthetically obtained R2pipdt (R = Me, iPr, Bz)/I3 salts, complemented by neutron diffraction experiments, were able to experimentally highlight the formation of [R2pipdtH]+ cations with a -S-H bond on the dithionic moiety. Differently, with R = Ph, a benzothiazolylium cation, resulting from an intramolecular condensation reaction of the ligand, is obtained. Based on density functional theory (DFT) calculations, a reasonable reaction mechanism where diiodine plays the fundamental role of promoting a halogen-bonding-mediated radical reaction has been proposed. In addition, the comparison of combined experimental and computational results with the corresponding reactions of N,N'-dialkylperhydrodiazepine-2,3-dithione (R2dazdt, a hepta-atomic cyclic dithiooxamide), which provide neutral halogen-bonded adducts, pointed out that the difference in the torsion angle of the free ligands represents the structural key factor in determining the different reactivities of the two systems.

Synthesis of a diruthenium μ-η4-α-diimine complex via dehydrogenative coupling of cyclic amines and its role in dehydrogenative oxidation of pyrrolidine.

The reaction of [Cp‡Ru(μ-H)4RuCp‡] (1: Cp‡ = 1,2,4-tri-tert-butylcyclopentadienyl) with cyclic amines at 180 °C afforded a μ-η4-α-diimine complex, [(Cp‡Ru)2(μ-η4-C2nH4n-4N2)] (5a-c: n = 4, 5, 6), via dehydrogenative coupling of two cyclic amine molecules. An intermediate μ-η2-1-pyrroline complex, [{Cp‡Ru(μ-H)}2(μ-η2-C4H7N)] (2a), was synthesized by the photoreaction of 1 with pyrrolidine and 5a was shown to be formed via the disproportionation of 2a upon thermolysis yielding 1 and a μ-imidoyl complex, [(Cp‡Ru)2(μ-η2:η2-C4H6N)(μ-H)] (3a). Complex 3a was transformed into 5avia the incorporation of 1-pyrroline, which was formed by the reaction of 2a with H2. DFT calculations on the model complexes supported by C5H5 groups at the B3LYP level suggested that the μ-η4-α-diimine ligand is formed via the insertion of a terminal cyclic aminocarbene ligand into the Ru-C bond of the μ-imidoyl group followed by the elimination of hydrogen. Although 5a was inert under an Ar atmosphere, it catalyzed the dehydrogenative oxidation of pyrrolidine under an atmosphere of hydrogen to yield γ-butyrolactam. An active species possessing a terminal cyclic aminocarbene ligand was generated via the heterolytic activation of hydrogen at the Ru-N bond followed by C-C bond cleavage.

A UOF based on a cyclotriphosphazene skeleton: fluorescence sensing of different substituted aldehydes and NACs.

A novel uranyl organic framework (U-hdpcp) based on flexible cyclic triphosphazene polycarboxylate ligands was prepared, which possesses the ability to sense aromatic aldehyde solutions (benzaldehyde, salicylaldehyde and 2-bromobenzaldehyde) and nitro compounds (2,4,6-trinitrophenol, 2,4-dinitrophenol and o-nitrophenol). A fluorescent thin film based on U-hdpcp@PVA with the ability to sense aldehyde vapors was prepared via a spin coating method. The work expands the library of UOF materials based on large-sized carboxylic acid ligands and demonstrates promising applications in the field of fluorescent sensors.