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The ability to collectively program chiral recognition and the hierarchical self-assembly of molecular and supramolecular building blocks into complex higher-order superstructures is a significant goal in supramolecular chemistry. Metal-organic cages are excellent model systems to examine chiral self-sorting and build hierarchical self-assembly. Herein, details on how limiting the conformational flexibility and incorporating hydrogen bonding functional groups in the ligands can influence chiral self-sorting and hierarchical self-assembly of metal-organic cages are reported. The urea-functionalized axially chiral bis-pyridyl ligands afford high-fidelity in chiral self-sorting in Pd2L4 cages, when they have fewer conformations. Ligand L1, with more conformations, affords mixture of heterochiral and homochiral cages (≈70:30). Among them, the heterochiral cage adopts unusual twisted conformation and self-assembles into 2D sheets, linked by anion coordination between urea and nitrate. Ligand L2, with fewer conformations, affords homochiral cages via high-fidelity chiral self-sorting. The choice of counter anions influences further self-sorting in the solid state: racemate with PF6 - and spontaneously resolves conglomerate with BF4 -. Urea-BF4 hydrogen bonding directs hierarchical self-assembly of the Pd2L4 metal-organic cages into super-cubic networks. The study introduces a new approach in hierarchical self-assembly of metal-organic cages into higher-order networks aided by hydrogen bonding anion coordination with functional ligands.
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Water-soluble organic cages are attractive targets for their molecular recognition and sensing features of biologically relevant molecules. Here, we have successfully designed and synthesized a pair of water-soluble cationic cages employing click reaction as the fundamental step followed by the N-methylation of the triazole rings. The rigid and shape-persistent 3D hydrophobic cavity, positively charged surface, H-bonding triazolium rings, and excellent water solubility empower both cages to exhibit a superior affinity and selectivity for binding with adenosine-5'-triphosphate (ATP) compared to cyclophanes and other macrocyclic receptors. Both cage molecules (PCCâ Cl and BCCâ Cl) can bind a highly emissive dye HPTS (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt) to form non-fluorescent complexes. The addition of ATP resulted in the stronger cageâATP complexes with the retention of HPTS emission upon its displacement. The resultant indicator-displacement assay system can efficiently sense and quantify ATP in nanomolar detection limits in buffer solutions and human serum matrix. Spectroscopic and theoretical studies revealed the synergistic effect of πâ â â π stacking interaction between the aromatic moiety of the cationic cages and the adenine moiety of ATP, as well as the electrostatic and hydrogen bonding interaction between the phosphate anion of ATP and triazole protons of cages, played the pivotal roles in the sensing process.
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Adenina , Adenosina Trifosfato , Humanos , Bioensayo , Ciclofanos , Protones , TriazolesRESUMEN
Developing synthetic supramolecular receptors to solubilize, scavenge, recognize, encapsulate, and sense steroids is challenging. Despite a limited number of receptors having affinity with steroids, none exists to bind steroidal bile acids selectively. Herein, we report a C2-symmetric metal-organic cage [Pd6L24]12+ and an expanded version of the Fujita cage [Pd6L14]12+, built with a conformationally flexible ligand L2, accessed through coordination-driven self-assembly. We examined both cages for steroid recognition in water: both have certain shared characteristics and distinctive features. [Pd6L14]12+ binds hydrophobic bile acids and other steroids by forming a 1:1 complex. In contrast, the expanded [Pd6L24]12+ cage exhibits an affinity for amphiphilic bile acids and selective steroids to encapsulate them as dimers, promoted by cooperative interguest hydrogen bonding. [Pd6L24]12+ has a 5 times stronger solubility enhancement ability for cholic acid compared to [Pd6L14]12+. Further, the expanded [Pd6L24]12+ cage can selectively sense bile acids in nanomolar detection limits through indicator displacement assay by employing sulforhodamine 101 (SR101).
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Ácidos y Sales Biliares , Ácidos y Sales Biliares/química , Estructuras Metalorgánicas/química , Paladio/química , Estructura MolecularRESUMEN
There is a strong and urgent need for efficient materials that can capture radioactive iodine atoms from nuclear waste. This work presents a novel strategy to develop porous materials for iodine capture by employing halogen bonding, mechanochemistry and crystal engineering. 3D halogen-bonded organic frameworks (XOFs) with guest-accessible permanent pores are exciting targets in crystal engineering for developing functional materials, and this work reports the first example of such a structure. The new-found XOF, namely TIEPE-DABCO, exhibits enhanced emission in the solid state and turn-off emission sensing of acid vapors and explosives like picric acid in nanomolar quantity. TIEPE-DABCO captures iodine from the gas phase (3.23 g g-1 at 75 °C and 1.40 g g-1 at rt), organic solvents (2.1 g g-1 ), and aqueous solutions (1.8 g g-1 in the pH range of 3-8); the latter with fast kinetics. The captured iodine can be retained for more than 7 days without any leaching, but readily released using methanol, when required. TIEPE-DABCO can be recycled for iodine capture several times without any loss of storage capacity. The results presented in this work demonstrate the potential of mechanochemical cocrystal engineering with halogen bonding as an approach to develop porous materials for iodine capture and sensing.
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When a racemic mixture of chiral building blocks self-assembles to form discrete molecular or supramolecular cages, the system can adopt either social or narcissistic chiral self-sorting. However, control over such chiral self-sorting is hard to achieve with a desired choice of outcome. Herein, we report anion templated high-fidelity chiral self-sorting during the coordination-driven self-assembly of [Pd2 L4 ] metal-organic cages, with a racemic mixture of an axially chiral ligand. Upon varying the counter-anions, the outcome of the choice of chiral self-sorting, whether social or narcissistic, leading to kinetically favored heterochiral or thermodynamically favored homochiral cages, can be controlled through specific anion encapsulation. Non-encapsulating anion afforded a mixture of all possible diastereomers. Anion exchange enabled structural transformations between the diastereomers and the conversion of the mixture of diastereomers into homochiral diastereomers.
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This study reports the synthesis of cofacial organic cage molecules containing aggregation-induced emissive (AIE) luminogens (AIEgens) through four-fold Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) "click" reactions. The shorter AIEgen, tetraphenylethylene (TPE), afforded two orientational isomers (TPE-CC-1A and TPE-CC-1B). The longer AIEgen, tetrabiphenylethylene (TBPE), afforded a single isomer (TBPE-CC-2). The click reaction employed is irreversible, yet it yielded remarkable four-fold click products above 40 %. The phenyl rings around the ethylene core generate propeller-shaped chirality owing to their orientation, which influences the chirality of the resulting cages. The shorter cages are a mixture of PP/MM isomers, while the longer ones are a mixture of PM/MP isomers, as evidenced by their x-ray structures. The newly synthesized cage molecules are emissive even in dilute solutions (THF) and exhibit enhanced AIE upon the addition of water. The aggregated cage molecules in aqueous solution exhibit turn-off emission sensing of nitroaromatic explosives, with selectivity to picric acid in the 25-38 nanomolar detection range.
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A facile, multicomponent (MCR) atom-economic synthesis of novel spiro-oxindolo pyrrolizidine adducts of piperine has been achieved via an intermolecular 1,3-dipolar azomethine ylide cycloaddition reaction. Either of the two conjugated double bonds in piperine takes part in the reaction to produce two regioisomeric adducts in racemic form. Acenaphthoquinone, ninhydrin and different isatin derivatives were reacted with proline and piperine to afford a never before reported library of 22 compounds. The structures of the products were determined by 1D/2D NMR, mass spectral analysis and confirmed by X-ray crystallography of selected products. Chiral HPLC separation was performed to measure the specific rotation and CD spectra of the enantiomers for two racemic compounds.
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Alcaloides/química , Compuestos Azo/química , Benzodioxoles/química , Oxindoles/química , Oxindoles/síntesis química , Piperidinas/química , Alcamidas Poliinsaturadas/química , Pirroles/química , Compuestos de Espiro/química , Tiosemicarbazonas/química , Reacción de Cicloadición , Modelos Moleculares , Conformación Molecular , EstereoisomerismoRESUMEN
We report about the coordination-driven self-assembly of a chiral bis-pyridyl ligand (1), synthesized from steroidal cholic acid, with Pd(II) ions to form a chiral metal-organic Pd2(1)4 cage. The self-assembly of the cage was facilitated by favorable conformational change in the alkyl chain of the cholic acid. Interligand hydrogen bonding played a crucial role in directing the formation of a C4 symmetric cage among different possible isomers, as suggested by DFT studies, and control experiments with different ligands.
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The ligand L1 of 4-methyl-2,6-diformylphenol and L2 of 4- tert-butyl-2,6-diformylphenol are synthesized through Schiff base condensation with rac-, ( R)-(+), or ( S)-(-)-1,1'-binaphthyl-2,2'-diamine (BNDA). As a result, the racemic L1rac, L2rac, and enantiopure L1RR, L1SS, L2RR, and L2SS ligands are obtained incorporating Cu(II) and Zn(II) salts by a simple one-pot metal template method. The series of dinuclear complexes of [M2LX2] (here, M = Cu2+, Zn2+; X = acetate ion, chloride ion; L = L1RR, L1SS, L1rac, L2RR, L2SS, L2rac) formulas are obtained in common. Among them, the single crystal X-ray structures for [Zn2L1rac(OAc)2] and [Zn2L1SSCl2] complexes are obtained. The detailed crystal structure and the chiroptical studies performed on these complexes dictates a self-sorting behavior in their self-assembly process and illustrate a chirality transfer from the ligand to the metal center on the complexes. The enantiopure dinuclear complexes [M2LRRX2] and [M2LSSX2] generate enantiopure ΛΛ and ΔΔ isomers, respectively, but the racemic complexes produce only homochiral ΛΛ and ΔΔ assemblies. The detailed studies based on UFLC (Ultra Fast Liquid Chromatography), CD, and single crystal X-ray structure together show the absence of heterochiral ΛΔ mesocate. All these complexes are adapted as catalysts for desymmetrization of various mesodiols, and the enantiopure complexes are found to give efficient enantioselectivity in desymmetrization of mesodiols with benzoyl chloride to monobenzoylated ester providing 98% yield and 92% ee.
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A readily accessible D-A-D triad molecule 1 was synthesized through acylhydrazone bond formation using carefully chosen building blocks. The molecule 1 exhibits emission through charge-coupled proton transfer and enhanced emission induced through aggregation and mechanochromic luminescence. Further, it detects Al(III) selectively among other cations in an efficient manner.
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A series of double-stranded binuclear helicates [Co2(H1)2]4+, [Co2(H2)2]4+, and [Co2(H3)2]4+, derived from monodeprotonated bis-pyridyl hydrazine-based ligands of H21, H22, and H23 with one, two, and three -CH2 spacers, were obtained. These asymmetric-carbon-free racemic helicates were separated into their ΔΔ and ΛΛ enantiomers. The resolved helicates were examined for the first time as enantioselective catalysts in asymmetric benzoylation and nitroaldol reactions.
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A palladium-catalyzed expeditious synthesis of dibenzofused carbazoles from readily available 2-arylindoles and diaryliodonium salts is reported. Interestingly, after the electrophilic C3 palladation of indole, an unexpected "through-space" 1,4-palladium migration to the 2-aryl moiety, by remote C-H bond activation followed by C-H arylation with diaryliodonium salt, and an unprecedented 1,2-aryl shift take place. Finally, an intramolecular cross-dehydrogenative coupling (CDC) at the C2 position affords dibenzo[a,c]carbazoles in high yields. Remarkably, the present migratory annulation occurs through three C-H bond activation one C-C bond cleavage, and the simultaneous construction of three new C-C bonds in a single operation.
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The potential of ß,γ-unsaturated α-ketothioesters participating in hetero-Diels-Alder reaction has remained unexplored. We report herein the first study of a ZnI2-catalyzed highly diastereoselective inverse electron demand hetero-Diels-Alder reaction of ß,γ-unsaturated α-ketothioesters with olefins to access highly substituted 3,4-dihydro-2H-pyrans. All the reactions proceed with cis-selectivity in moderate to excellent yields. Under similar reaction conditions, terminal alkynes undergo direct conjugate 1,4-addition to yield δ,ε-acetylenic α-ketothioesters. Furthermore, the utility of these cycloadducts has been demonstrated by an NBS-MeOH mediated stereospecific efficient access to fully substituted pyran rings. The product bromoethers undergo E2 elimination with DBU, resulting in substituted 3,6-dihydro-2H-pyrans. In addition, the thioester moiety of the products has been used for further transformations, such as amidations and Fukuyama coupling reactions.
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Alquenos/química , Ésteres/química , Yoduros/química , Compuestos de Sulfhidrilo/química , Compuestos de Zinc/química , Catálisis , Ciclización , Estructura Molecular , EstereoisomerismoRESUMEN
Cucurbit[7]uril (CB[7]), an uncharged and water-soluble macrocyclic host, binds protonated amino saccharides (D-glucosamine, D-galactosamine, D-mannosamine and 6-amino-6-deoxy-D-glucose) with excellent affinity (Ka =10(3) to 10(4) M(-1) ). The host-guest complexation was confirmed by NMR spectroscopy, isothermal titration calorimetry (ITC), and MALDI-TOF mass spectral analyses. NMR analyses revealed that the amino saccharides, except D-mannosamine, are bound as α-anomers within the CB[7] cavity. ITC analyses reveal that CB[7] has excellent affinity for binding amino saccharides in water. The maximum affinity was observed for D-galactosamine hydrochloride (Ka =1.6×10(4) M(-1) ). Such a strong affinity for any saccharide in water using a synthetic receptor is unprecedented, as is the supramolecular stabilization of an α-anomer by the host.
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Hidrocarburos Aromáticos con Puentes/química , Carbohidratos/química , Imidazoles/química , Sustancias Macromoleculares/química , Conformación Molecular , Agua/químicaRESUMEN
Intending to homogenize the biological activities of both quinoxaline and imidazole moieties, the proligand, 1-methyl-3-quinoxaline-imidazolium hexaflurophosphate (1.HPF6), and [Ag(1)2][PF6], (2); [Au(1)2][PF6], (3); and [Au(1)Cl3], (4) NHC complexes were synthesized. All the synthesized compounds were characterized by elemental analysis, NMR, and UV-Vis spectroscopy. Finally, single crystal X-ray structures revealed a linear geometry for complex 2 whereas a square planar geometry for complex 4. The formation of complex 3 was confirmed and supported by its MS spectra. The antibacterial activities of all the synthesized complexes were investigated against gram-positive bacteria and gram-negative bacteria. The Au(III)-NHC complex, 4 showed the highest antibacterial activity with extremely low MIC values against both the bacterial strains (0.24â µg mL-1). Monitoring of zeta potential supports the higher activity of complex 4 compared to 2 and 3. ROS production by complex 4 has also been measured inâ vitro in the CT26 cancer cell lines, which is directly responsible for targetting and killing the bacterial pathogens. Cell cytotoxicity assay using 293T cell lines has been performed to investigate the biocompatibility nature of complex 4. Also, an excellent hemocompatibility was assigned to it from its hemolytic studies, which provide valuable insights into the design of novel antibacterial agents.
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A pyridine functionalized pyrimidine-based system, H2P was successfully synthesized, characterized, and evaluated for its remarkable selective characteristics towards Zn2+ and ATP ions. The chemical sensing capabilities of H2P were demonstrated through absorption, fluorescence, and NMR spectroscopic techniques. The probe exhibited outstanding sensitivity when interacting with the ions, demonstrating relatively strong association constants and impressively low detection limits. The comprehensive binding mechanism of H2P with respect to Zn2+ and ATP ions was investigated using a combination of analytical methods, including Job's plot, NMR spectroscopy, mass spectrometry, and density functional theory (DFT) experiments. The interesting sensing ability of H2P for Zn2+/ATP ions was harnessed for live cell bioimaging and other diverse on-site detection purposes, including paper strips, cotton swabs, and applications involving mung bean sprouts. Further, the fluorescent probe demonstrated its effectiveness in detecting Zn2+ and ATP within live cells, indicating its significant potential in the realm of biological imaging applications. Moreover, the molecular configuration of the zinc complex (H2P-Zn2Cl4), derived from H2P, was elucidated using X-ray crystallography. This complex exhibited intriguing multifunctional attributes, encompassing its capability for detecting picric acid and for reversible acid/base sensing responses. The enhanced conducting behavior of the complex as well as its resistance properties were investigated by performing I-V characteristics and electrochemical impedance spectroscopic (EIS) experiments respectively.
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Piridinas , Zinc , Zinc/química , Pirimidinas , Iones/análisis , Adenosina Trifosfato , Colorantes Fluorescentes/química , Espectrometría de FluorescenciaRESUMEN
Previous work has shown that certain steroidal bis-(N-phenyl)ureas, derived from cholic acid, form crystals in the P6(1) space group with unusually wide unidimensional pores. A key feature of the nanoporous steroidal urea (NPSU) structure is that groups at either end of the steroid are directed into the channels and may in principle be altered without disturbing the crystal packing. Herein we report an expanded study of this system, which increases the structural variety of NPSUs and also examines their inclusion properties. Nineteen new NPSU crystal structures are described, to add to the six which were previously reported. The materials show wide variations in channel size, shape, and chemical nature. Minimum pore diameters vary from ~0 up to 13.1 Å, while some of the interior surfaces are markedly corrugated. Several variants possess functional groups positioned in the channels with potential to interact with guest molecules. Inclusion studies were performed using a relatively accessible tris-(N-phenyl)urea. Solvent removal was possible without crystal degradation, and gas adsorption could be demonstrated. Organic molecules ranging from simple aromatics (e.g., aniline and chlorobenzene) to the much larger squalene (M(w) = 411) could be adsorbed from the liquid state, while several dyes were taken up from solutions in ether. Some dyes gave dichroic complexes, implying alignment of the chromophores in the NPSU channels. Notably, these complexes were formed by direct adsorption rather than cocrystallization, emphasizing the unusually robust nature of these organic molecular hosts.
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Here, we report a simple, efficient, and green protocol for the one-pot synthesis of pyrano[2,3-c]pyrazole derivatives via a sequential three-component strategy using aromatic aldehydes, malononitrile and pyrazolin-5-one in a water-SDS-ionic liquid system. This is a base and volatile organic solvent-free approach that could be applicable to a wide substrate scope. The key advantages of the method over other established protocols are very high yield, eco-friendly conditions, chromatography-free purification and recyclability of the reaction medium. Our study revealed that the N-substituent present in pyrazolinone controls the selectivity of the process. N-unsubstituted pyrazolinone favours the formation of 2,4-dihydro pyrano[2,3-c]pyrazoles whereas under identical conditions N-phenyl substituent pyrazolinone favours the formation 1,4-dihydro pyrano[2,3-c]pyrazoles. Structures of the synthesized products were established by NMR and X-ray diffraction techniques. Energy optimized structures and energy gaps between the HOMO-LUMO of some selected compounds were estimated using density functional theory to explain the extra stability of the 2,4-dihydro pyrano[2,3-c]pyrazoles over 1,4-dihydro pyrano[2,3-c]pyrazoles.
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The design and synthesis of a cleft-shaped bis-diarylurea receptor for chloride anion transport is reported in this work. The receptor is based on the foldameric nature of N,N'-diphenylurea upon its dimethylation. The bis-diarylurea receptor exhibits a strong and selective affinity for chloride over bromide and iodide anions. A nanomolar quantity of the receptor efficiently transports the chloride across a lipid bilayer membrane as a 1:1 complex (EC50 = 5.23 nm). The work demonstrates the utility of the N,N'-dimethyl-N,N'-diphenylurea scaffold in anion recognition and transport.
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Chiral self-sorting during the formation of cage-like molecules continues to fascinate and advance our understanding of the phenomenon in general. Herein, we report the chiral self-sorting in the Pd6 L12 -type metal-organic cages. When a racemic mixture of axially chiral bis-pyridyl ligands undergo coordination-driven self-assembly with Pd(II) ions to form Pd6 L12 -type cages, the system has the option of chiral self-sorting to afford any of at least 70 pairs of (one homochiral and 69 heterochiral) enantiomers and 5 meso isomers or a statistical mixture of everything. However, the system resulted in diastereoselective self-assembly through a high-fidelity chiral social self-sorting to form a racemic mixture of D3 symmetric heterochiral [Pd6 (L6R/6S )12 ]12+ /[Pd6 (L6S/6R )12 ]12+ cages.