Synthesis, structure and photophysical properties of pyrene–based [5]helicenes : an experimental and theoretical study

Pyrene-cored [5]helicenes were prepared by a facile, efficient Wittig reaction and an intramolecular photocyclization reaction utilising 2,7-di-tert-butylpyrene-4-carbaldehyde and naphthalene/pyrene-based phosphorus ylides. Optical properties based on UV−vis absorption and fluorescence spectra were investigated. X-ray crystallography revealed that the pyrene-based [5]helicenes exhibited strong face-to-face π−π interactions and edge-to-face π−π interactions. HOMO and LUMO energies and molecular orbitals were also studied by density functional theory (DFT) calculations. This study has revealed that the torsion angle of the helical structure plays a role in determining the π−π interactions and the frontier molecular orbital energy levels. Thus, pyrene-based helicenes need to be considered when one designs new highly efficient organic light-emitting diodes and organic semiconductor materials

Investigating the role of lymph node stromal cells and miR-132 in regulating TLR4 agonist adjuvant efficacy

Lymph nodes (LNs) are highly organized structures containing adaptive and innate immune cells supported by a network of specialized stromal cells. These stromal cells provide the structural basis for immune cell migration, localization and specialized microenvironments for effector function through the production of specific chemokines. Crosstalk between stroma and haematopoietic cells is important in regulating the efficacy of the immune response in part through their plastic response to inflammation and capacity to generate specialized structures, including germinal centres (GCs). The mechanisms driving tissue remodelling and GC formation in LNs are unclear. Understanding the timing and molecular mechanisms leading to stromal cell reorganization will help generate novel vaccination strategies that can control and regulate immune responses. An adjuvant is a non-antigenic substance that when added to vaccines, enhances the immune response to inoculated antigens. TLR agonists have been shown to be potent second-generation adjuvants. TLR4 agonist adjuvants induce rapid LN remodelling through the loss of B cell follicles and the formation of a ring-like structure in the cortex; surprisingly this was not due to a loss of CXCL13 production by the stromal cells. After forming this ring, large numbers of new B cell follicles appear in the LN paracortex. The molecular mechanisms leading to this reorganization was investigated. TLR4 activation and signalling has to be tightly controlled to avoid uncontrolled inflammation and enable tissue repair. miRNAs constitute a key component in a negative feedback loop in innate immune responses. Deficiency in a TLR4-induced miRNA leads to an altered immune response and changes to adjuvant induced tissue remodelling. By using a simple antigen challenge model, it was possible to determine a novel molecular mechanism controlling LN remodelling and vaccine efficacy

Synthesis and Structure of 1,2-Dimethylene[2.10]metacyclophane and Its Conversion into Chiral [10]Benzenometacyclophanes: Synthesis and Structure of 1,2-Dimethylene[2.10]metacyclophane and Its Conversion into Chiral [10]Benzenometacyclophanes

Bromination of 5,21-di-tert-butyl-8,24-dimethoxy-1,2-dimethyl[2.10]metacyclophan-1-ene (MCP-1-ene; 1) with benzyltrimethylammonium tribromide exclusively afforded 1,2-bis(bromomethyl)-5,21-di-tert-butyl-8,24-dimethoxy[2.10]MCP-1-ene (2). Debromination of 2 with Zn and AcOH in CH₂Cl solution at room temperature for 24 h produced dimethylene[2.10]MCP 7 in 92 % yield, which is a stable solid compound. Compound 7 was treated with dimethyl acetylenedicarboxylate (DMAD) to provide 1,2-(3′,6′-dihydrobenzo)-5,21-di-tert-butyl-8,24-dimethoxy[2.10]MCP-4′,5′-dimethylcarboxylate (8) in good yield. Diels–Alder adduct 8 was converted into a novel and inherently chiral areno-bridged dimethoxy[2.10]MCP-4′,5′-dimethylcarboxylate 9, possessing C₁ symmetry, by aromatization with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). A new type of N-phenyl-maleimide substituted 1,2-(3′,6′-dihydrobenzo)-5,21-di-tert-butyl-8,24-dimethoxy[2.10]MCP-4′,5′-N-phenylmaleimide 10 was also synthesized from 7 through treatment with N-phenylmaleimide in toluene at 110 °C followed by aromatization with DDQ. Single-crystal X-ray analysis of 9 revealed the formation of a syn-isomer

Synthesis and conformational studies of calixarene analogue chiral [3.3.1]metacyclophanes

Trihydroxy[3.3.1]metacyclophane, which can be regarded as an unsymmetrical or incomplete “homocalix[3]arene”, has been prepared from trimethoxy[3.3.1]metacyclophane by demethylation with trimethylsilyl iodide in MeCN. Di-O-methylation at the lower rim of trihydroxy[3.3.1]metacyclophane in the presence of K₂CO₃ in acetone afforded a novel, inherently chiral calixarene–analogue, namely a macrocyclic [3.3.1]metacyclophane, possessing C₁ symmetry. The inherent chirality of the two conformers was characterized by ¹H NMR spectroscopy by addition of an excess of Pirkle's chiral shift reagent [(S)-(+)-1-(9-anthryl)-2,2,2-trifluoroethanol], which caused a splitting of the OMe group and AB patterns corresponding to the methylene protons

Copper coordination polymers from cavitand ligands: hierarchical spaces from cage and capsule motifs, and other topologies

The cyclotriveratrylene-type ligands (±)-tris(iso-nicotinoyl)cyclotriguaiacylene L1 (±)-tris(4-pyridylmethyl)cyclotriguaiacylene L2 and (±)-tris{4-(4-pyridyl)benzyl}cyclotriguaiacylene L3 all feature 4-pyridyl donor groups and all form coordination polymers with CuI and/or CuII cations that show a remarkable range of framework topologies and structures. Complex [CuI4CuII1.5(L1)3(CN)6]·CN·n(DMF) 1 features a novel 3,4-connected framework of cyano-linked hexagonal metallo-cages. In complexes [Cu3(L2)4(H2O)3]·6(OTf)·n(DMSO) 2 and [Cu2(L3)2Br2(H2O)(DMSO)]·2Br·n(DMSO) 3 capsule-like metallo-cryptophane motifs are formed which linked through their metal vertices into a hexagonal 2D network of (43.123)(42.122) topology or a coordination chain. Complex [Cu2(L1)2(OTf)2(NMP)2(H2O)2]·2(OTf)·2NMP 4 has an interpenetrating 2D 3,4-connected framework of (4.62.8)(62.8)(4.62.82) topology with tubular channels. Complex [Cu(L1)(NCMe)]·BF4·2(CH3CN)·H2O 5 features a 2D network of 63 topology while the CuII analogue [Cu2(L1)2(NMP)(H2O)]·4BF4·12NMP·1.5H2O 6 has an interpenetrating (10,3)-b type structure and complex [Cu2(L2)2Br3(DMSO)]·Br·n(DMSO) 7 has a 2D network of 4.82 topology. Strategies for formation of coordination polymers with hierarchical spaces emerge in this work and complex 2 is shown to absorb fullerene-C60 through soaking the crystals in a toluene solution

Tetra­kis(μ-3-aza­niumylbenzoato)-κ3 O:O,O′;κ3 O,O′:O;κ4 O:O′-bis­[triaqua­chloridolanthanum(III)] tetra­chloride dihydrate

The tiltle complex, [La2(C7H7NO2)4Cl2(H2O)6]Cl4·2H2O, is a centrosymmetric dimer formed by edge-sharing LaO5(H2O)3Cl polyhedra linked together by a carboxyl­ate ligand. The two LaIII metal ions are linked by two bidentate bridging carboxyl­ate groups with a κ2 O:O′ coordination mode and two bidentate chelating bridging carboxyl­ate groups with a κ3 O:O,O′ coordination mode. The coordination sphere of lanthanum, completed by a terminal chloride and three water mol­ecules, adopts a distorted tricapped trigonal–prismatic arrangement. N—H⋯Cl, N—H⋯O and O—Hwater⋯Cl hydrogen bonds, and slipped π–π inter­actions between parallel benzene rings [centroid–centroid distance of 3.647 (3) Å] are observed in the structure. These combine to stabilize a three-dimensional network

Alkali metal derivatives of an ortho-phenylene diamine

Treatment of the ortho-phenylene diamine C6H4-1,2-{N(H)Tripp}2 (1, PDAH2, Tripp = 2,4,6-triisopropylphenyl) with two equivalents of MR (M = Li, R = Bun; M = Na or K, R = CH2C6H5) afforded the dimetallated alkali metal ortho-phenylene diamide dianion complexes [(PDALi2)(THF)3] (2), [{(PDANa2)(THF)2}2] (3), and [{(PDAK2)(THF)3}2] (4). In contrast, treatment of 2 with two equivalents of rubidium or cesium 2-ethylhexoxide, or treatment of 1 with two equivalents of MR (M = Rb or Cs, R = CH2C6H5) did not afford the anticipated dialkali metal ortho-phenylene diamide dianion derivatives and instead formally afforded the monometallic ortho-diiminosemiquinonate radical anion species [PDAM] (M = Rb, 5; M = Cs, 6). The structure of 2 is monomeric with one lithium coordinated to the two nitrogen centres and the other lithium η4-coordinated to the diazabutadiene portion of the PDA scaffold. Similar structural cores are observed for 3 and 4, except that the larger sodium and potassium ions give dimeric structures linked by multi-hapto interactions from the PDA backbone phenyl ring to an alkali metal centre. Complex 5 was not characterised in the solid state, but the structure of 6 reveals coordination of cesium ions to both PDA amide centres and multi-hapto interactions to a PDA backbone phenyl ring in the next unit to generate a one-dimensional polymer. Complexes 2–6 have been variously characterised by X-ray crystallography, multi-nuclear NMR, FTIR, and EPR spectroscopies, and CHN microanalyses

B-cell Zone Reticular Cell Microenvironments Shape CXCL13 Gradient Formation

Through the formation of concentration gradients, morphogens drive graded responses to extracellular signals, thereby fine-tuning cell behaviors in complex tissues. Here we show that the chemokine CXCL13 forms both soluble and immobilized gradients. Specifically, CXCL13+ follicular reticular cells form a small-world network of guidance structures, with computer simulations and optimization analysis predicting that immobilized gradients created by this network promote B-cell trafficking. Consistent with this prediction, imaging analysis show that CXCL13 binds to extracellular matrix components in situ, constraining its diffusion. CXCL13 solubilization requires the protease cathepsin B that cleaves CXCL13 into a stable product. Mice lacking cathepsin B display aberrant follicular architecture, a phenotype associated with effective B cell homing to but not within lymph nodes. Our data thus suggest that reticular cells of the B cell zone generate microenvironments that shape both immobilized and soluble CXCL13 gradient

Accelerated microwave curing of fibre-reinforced thermoset polymer composites for structural applications: A review of scientific challenges

Accelerated curing of high performance fibre-reinforced polymer (FRP) composites via microwave heating or radiation, which can significantly reduce cure time and increase energy efficiency, has several major challenges (e.g. uneven depth of radiation penetration, reinforcing fibre shielding, uneven curing, introduction of hot spots etc). This article reviews the current scientific challenges with microwave curing of FRP composites considering the underlying physics of microwave radiation absorption in thermoset-matrix composites. The fundamental principles behind efficient accelerated curing of composites using microwave radiation heating are reviewed and presented, especially focusing on the relation between penetration depth, microwave frequency, dielectric properties and cure degree. Based on this review, major factors influencing microwave curing of thermoset-matrix composites are identified, and recommendations for efficient cure cycle design are provided