Esmodil: an acetylcholine mimetic resurfaces in a Southern Australian marine sponge Raspailia (Raspailia) sp

Bioassay directed fractionation of a Raspailia (Raspailia) sp. (Order Poecilosclerida; Family Raspailiidae) collected during scientific trawling operations off the Northern Rottnest Shelf yielded as nematocidal agents the known metabolites, phorboxazoles A (1) and B (2). Further examination revealed the new natural product but known synthetic compound, esmodil (3). The structure for 3 was confirmed by spectroscopic analysis and total synthesis.     

Rational Topological Design for Fluorescence Enhancement upon Aggregation of Distyrylfuran Derivatives

A series of 2,5‐distyrylfuran derivatives bearing pentafluorophenyl‐ and cyanovinyl units have been synthesized for aggregation‐induced emission (AIE). The effect of the type and extent of the supramolecular connections on the AIE of the furan derivatives were examined and correlated with their X‐ray crystal structures. It was found that the simultaneous presence of cyano and perfluorophenyl units strongly enhances the fluorescence upon aggregation. Single‐crystal X‐ray diffraction analysis confirmed that C?H???F, F???F, C?H???nitrile, Ar???Ar_F (Ar=aryl, Ar_F=fluoroaryl), and nitrile???Ar_F intra‐ and intermolecular interactions drive the topology of the molecule and that solid‐state supramolecular contacts favor AIE of the furan derivatives.     

Synthesis and Characterization of Liquid-Crystalline Tetraoxapentacene Derivatives Exhibiting Aggregation-Induced Emission

A series of new tetrakis(dialkoxyphenyl) dicyanotetraoxapentacene derivatives ( 1 a – c ) were prepared by reaction of the appropriate terphenyl diols with tetrafluoroterephthalonitrile in good yields. Compounds 1 b and 1 c , which bear hexyloxy and decyloxy side chains, exhibited columnar hexagonal mesophases, as shown by polarized optical microscopy, variable-temperature powder X-ray diffraction, and differential scanning calorimetry. Single-crystal X-ray diffraction of methoxy-substituted 1 a revealed that the dicyanotetraoxapentacene core is highly planar, consistent with the notion that these molecules are able to stack in columnar mesophases. A detailed photophysical characterization showed that these compounds exhibit aggregation-induced emission in solution, emission in nonpolar solvents, weak emission in polar solvents, and strong emission in the solid state both as powder and in thin films. These observations are consistent with a weakly emissive charge-transfer state in polar solvents and a more highly emissive locally excited state in nonpolar solvents.     

Unsymmetric pyrrole, thiophene, and furan-conjugated comonomers prepared using azomethine connections: potential new monomers for alternating homocoupled products

Unsymmetric comonomers consisting of thiophene, pyrrole, and furan heterocycles were prepared using azomethine bonds. Photophysical investigation of the novel pi-donor-donor-donor segmented compounds revealed that their singlet excited state is only partially deactivated by internal conversion unlike their all-thiophene azomethine analogues. Temperature-dependent steady-state and time-resolved emission studies demonstrated that the unsymmetric compounds deactivated efficiently their singlet excited state by intersystem crossing to populate the triplet manifold. This lower energy state is rapidly deactivated by nonradiative self-quenching. The comonomers and their anodically prepared conjugated homocoupled products are both electrochemically active, resulting in new compounds that can be mutually oxidized and reduced. Meanwhile, the oxidation potentials of the coupled products are shifted by up to 400 mV to more cathodic potentials relative to their corresponding comonomers, confirming their increased degree of conjugation.     

α,α'-N-Boc-substituted bi- and terthiophenes: fluorescent precursors for functional materials

Fluorescent α,α'-diamide substituted bi- and terthiophene derivatives were prepared by Stille and Suzuki couplings. Their one-pot deprotection and coupling with 2-thiophene carboxaldehyde led to stable conjugated azomethines. These exhibited electrochromic properties, and they were used to fabricate a working electrochromic device.     

Crystal Structure of an EMAP‐II‐Like Cytokine Released from a Human tRNA Synthetase

Aminoacyl‐tRNA synthetases catalyze the first step of protein synthesis by aminoacylation of tRNAs. Remarkably, biological fragments of two human enzymes – tyrosyl‐tRNA synthetase (TyrRS) and tryptophanyl‐tRNA synthetase – are active cytokines produced by proteolysis or alternative splicing. One is a C‐terminal fragment of TyrRS (C‐TyrRS) that has potent activity for chemotaxis of leukocytes and monocytes and for stimulating production of other cytokines. Significantly, the cytokine activity of C‐TyrRS is absent in the context of the full‐length native protein. Unknown is the mechanism by which domain‐release from the dimeric native protein activates the cytokine. Here, the crystal structure of C‐TyrRS is presented at 2.2 Å resolution. This structure is similar to that of endothelial monocyte‐activating protein II (EMAP‐II), with critical residues of a heptapeptide element important for chemotaxis activity exposed on the first strand of a β‐barrel of the monomeric unit. In contrast, the same residues of C‐TyrRS are buried in an operational model for native TyrRS. Importantly, C‐TyrRS is shown here to be monomeric when released from dimeric native TyrRS. Further analysis suggests that the critical residues are exposed when tRNA is bound. Thus, tRNA binding to native TyrRS may be an additional or alternative way to activate cytokine signaling.     

Neutral and Charged Brushes Covalently Grafted from OH-Functionalized Mica Surfaces using Surface-Initiated ATRP – Swelling Investigation by AFM

Poly(acrylic acid) (PAA) and poly(tert-butyl acrylate) (PBA) brushes of various grafting densities were prepared via surface-initiated polymerization of tert-butyl acrylate on mica. PAA was prepared by hydrolyzing the PBA brushes. The swelling behavior of PBA and PAA brushes was studied as a function of grafting density by AFM. The swelling of the polymer layer was found to be higher for PAA in water than for the PBA sample swollen with DFM.     

Aspergillicins A-E: five novel depsipeptides from the marine-derived fungus Aspergillus carneus

A search for new antiparasitic agents from a strain of the fungus Aspergillus carneus isolated from an estuarine sediment collected in Tasmania, Australia, yielded the known terrestrial fungal metabolite marcfortine A (1) as an exceptionally potent antiparasitic agent. This study also yielded a series of new depsipeptides, aspergillicins A-E (2-6) and the known terrestrial fungal metabolite acyl aszonalenin (7). Marcfortine A (1) and acyl aszonalenin (7) were identified by spectroscopic analysis, with comparison to literature data. Complete stereostructures were assigned to aspergillicins A-E (2-6) on the basis of detailed spectroscopic analysis, together with ESIMS analysis of the free amino acids generated by acid hydrolysis, and HPLC analysis of Marfey derivatives prepared from the acid hydrolysate. The peptide amino acid sequence for all aspergillicins was unambiguously assigned by MS(n) ion-trap ESI mass spectrometry.     

Fluorescence from Samarium(II) Iodide and Its Electron Transfer Quenching: Dynamics of the Reaction of Benzyl Radicals with Sm(II)

The luminescence from SmI(2) in THF can be readily quenched by a variety of electron acceptors. In the case of organohalides, the reaction is quite fast; for example, for dichloromethane the rate constant is 2.7 x 10(8) M(-)(1) s(-)(1). Electron transfer leads to halide loss and formation of the carbon-centered radical. In the case of benzyl chloride, the benzyl radicals produced can be readily detected using laser flash photolysis techniques. This electron-transfer reaction has been used as a source of benzyl radicals in order to determine the rate constant for their reaction with SmI(2); the value obtained is (5.3 +/- 1.4) x 10(7) M(-)(1) s(-)(1) in THF at room temperature. The effect of HMPA on the spectroscopic properties of SmI(2) has also been examined.