Synthesis and characterisation of the new oxyselenide Bi2YO4Cu2Se2

In this communication we report the synthesis, structure and preliminary characterisation of Bi2LnO4Cu2Se2 (Ln = Y, Gd, Sm, Nd, La) phases; these materials are members of a new family of layered oxychalcogenides.     

Determining attenuation properties of interfering fast and slow ultrasonic waves in cancellous bone

Previous studies have shown that interference between fast waves and slow waves can lead to observed negative dispersion in cancellous bone. In this study, the effects of overlapping fast and slow waves on measurements of the apparent attenuation as a function of propagation distance are investigated along with methods of analysis used to determine the attenuation properties. Two methods are applied to simulated data that were generated based on experimentally acquired signals taken from a bovine specimen. The first method uses a time-domain approach that was dictated by constraints imposed by the partial overlap of fast and slow waves. The second method uses a frequency-domain log-spectral subtraction technique on the separated fast and slow waves. Applying the time-domain analysis to the broadband data yields apparent attenuation behavior that is larger in the early stages of propagation and decreases as the wave travels deeper. In contrast, performing frequency-domain analysis on the separated fast waves and slow waves results in attenuation coefficients that are independent of propagation distance. Results suggest that features arising from the analysis of overlapping two-mode data may represent an alternate explanation for the previously reported apparent dependence on propagation distance of the attenuation coefficient of cancellous bone.     

Separating electrophilicity and Lewis acidity: the synthesis, characterization, and electrochemistry of the electron deficient tris(aryl)boranes B(C6F5)(3-n)(C6Cl5)n (n = 1-3)

A new family of electron-deficient tris(aryl)boranes, B(C(6)F(5))(3-n)(C(6)Cl(5))(n) (n = 1-3), has been synthesized, permitting an investigation into the steric and electronic effects resulting from the gradual replacement of C(6)F(5) with C(6)Cl(5) ligands. B(C(6)F(5))(2)(C(6)Cl(5)) (3) is accessed via C(6)Cl(5)BBr(2), itself prepared from donor-free Zn(C(6)Cl(5))(2) and BBr(3). Reaction of C(6)Cl(5)Li with BCl(3) in a Et(2)O/hexane slurry selectively produced B(C(6)Cl(5))(2)Cl, which undergoes B-Cl exchange with CuC(6)F(5) to afford B(C(6)F(5))(C(6)Cl(5))(2) (5). While 3 forms a complex with H(2)O, which can be rapidly removed under vacuum or in the presence of molecular sieves, B(C(6)Cl(5))(3) (6) is completely stable to refluxing toluene/H(2)O for several days. Compounds 3, 5, and 6 have been structurally characterized using single crystal X-ray diffraction and represent the first structure determinations for compounds featuring B-C(6)Cl(5) bonds; each exhibits a trigonal planar geometry about B, despite having different ligand sets. The spectroscopic characterization using (11)B, (19)F, and (13)C NMR indicates that the boron center becomes more electron-deficient as n increases. Optimized structures of B(C(6)F(5))(3-n)(C(6)Cl(5))(n) (n = 0-3) using density functional theory (B3LYP/TZVP) are all fully consistent with the experimental structural data. Computed (11)B shielding constants also replicate the experimental trend almost quantitatively, and the computed natural charges on the boron center increase in the order n = 0 (0.81) < n = 1 (0.89) < n = 2 (1.02) < n = 3 (1.16), supporting the hypothesis that electrophilicity increases concomitantly with substitution of C(6)F(5) for C(6)Cl(5). The direct solution cyclic voltammetry of B(C(6)F(5))(3) has been obtained for the first time and electrochemical measurements upon the entire series B(C(6)F(5))(3-n)(C(6)Cl(5))(n) (n = 0-3) corroborate the spectroscopic data, revealing C(6)Cl(5) to be a more electron-withdrawing group than C(6)F(5), with a ca. +200 mV shift observed in the reduction potential per C(6)F(5) group replaced. Conversely, use of the Guttmann-Beckett and Childs' methods to determine Lewis acidity on B(C(6)F(5))(3), 3, and 5 showed this property to diminish with increasing C(6)Cl(5) content, which is attributed to the steric effects of the bulky C(6)Cl(5) substituents. This conflict is ascribed to the minimal structural reorganization in the radical anions upon reduction during cyclic voltammetric experiments. Reduction of 6 using Na((s)) in THF results in a vivid blue paramagnetic solution of Na(+) [6](?-); the EPR signal of Na(+)[6](?-) is centered at g = 2.002 with a((11)B) 10G. Measurements of the exponential decay of the EPR signal (298 K) reveal [6](?-) to be considerably more stable than its perfluoro analogue.     

Ligand Bite Angle‐Dependent Palladium‐Catalyzed Cyclization of Propargylic Carbonates to 2‐Alkynyl Azacycles or Cyclic Dienamides

The regioselectivity of the palladium‐catalyzed cyclization of propargylic carbonates with sulfonamide nucleophiles is critically dependent on the bite angle of the bidentate phosphine ligand. Ligands with small bite angles favor attack on the central carbon atom of an allenylpalladium intermediate to afford cyclic dienamide products, whereas the use of those with large bite angles leads to alkynyl azacycles, with high stereoselectivity. A computational analysis of the reaction pathway is also presented.     

Diphenylacetylene‐Linked Peptide Strands Induce Bidirectional β‐Sheet Formation

In the search for synthetic mimics of protein secondary structures relevant to the mediation of protein–protein interactions, we have synthesized a series of tetrasubstituted diphenylacetylenes that display β‐sheet structures in two directions. Extensive X‐ray crystallographic and NMR solution phase studies are consistent with these proteomimetics adopting sheet structures, displaying both hydrophobic and hydrophilic amino acid side chains.     

A Series of Potent CREBBP Bromodomain Ligands Reveals an Induced‐Fit Pocket Stabilized by a Cation–π Interaction

The benzoxazinone and dihydroquinoxalinone fragments were employed as novel acetyl lysine mimics in the development of CREBBP bromodomain ligands. While the benzoxazinone series showed low affinity for the CREBBP bromodomain, expansion of the dihydroquinoxalinone series resulted in the first potent inhibitors of a bromodomain outside the BET family. Structural and computational studies reveal that an internal hydrogen bond stabilizes the protein‐bound conformation of the dihydroquinoxalinone series. The side chain of this series binds in an induced‐fit pocket forming a cation–π interaction with R1173 of CREBBP. The most potent compound inhibits binding of CREBBP to chromatin in U2OS cells.     

Determination of the solubilising character of 2-methoxyethyl-(dimethyl)ethylammonium tris(pentafluoroethyl)trifluorophosphate based on the Abraham solvation parameter model

Gas–liquid chromatographic retention factors have been measured for 42 different organic probes on a 2-methoxyethyl(dimethyl)ethylammonium tris(pentafluoroethyl)trifluorophosphate, ([MeoeM₂EAm]⁺[FAP]^–), stationary phase capillary column at 323 and 353 K. The measured retention factors were combined with published gas-to-liquid partition coefficient data for solutes dissolved in ([MeoeM₂EAm]⁺[FAP]^–) and with published gas-to-water partition coefficient data to yield 107 gas-to-anhydrous ionic liquid and 105 water-to-anhydrous ionic liquid partition coefficients. Abraham model correlations for describing solute transfer into ([MeoeM₂EAm]⁺[FAP]^–) were derived from the three sets of experimental partition coefficient data. The derived correlations back-calculated the experimental gas-to-([MeoeM₂EAm]⁺[FAP]^–) and water-to-([MeoeM₂EAm]⁺[FAP]^–) partition coefficient data to within 0.13 and 0.15 log units, respectively.     

Highly conducting transmembrane pores formed by aromatic oligoamide macrocycles

Oligoamide macrocycles 1d and 1e, which carry membrane-compatible side chains and contain a hydrophilic, noncollapsible cavity, were found to mediate high ion flux across a lipid bilayer, as demonstrated by results from (23)Na NMR and planar bilayer conductance measurements. The measured transmembrane single channel currents are very high, rivaling those typically associated with pore-forming protein toxins. The obtained results have demonstrated the promise of developing large, highly conducting channels based on nanopores formed by oligoamide macrocycles.