Reaction of aryl chromium carbene complexes with ethyl propiolate a versatile vinyl ether formation

Arylmethoxychromium-carbene complexes reacted with ethyl propiolate in the presence of alcohol to form and yields of aryl vinyl ether derivatives of malonate.     

Muon spin relaxation study on magnetism in high quality single crystal of a high transition temperature superconductor La2−xSrxCuO4−σ (0.11≤x≤0.14)

The positive muon spin relaxation method is applied to probe magnetic ordering in the superconducting phase of a high quality single crystal of La_2−xSr_xCuO_4−σ (0.11≤x≤0.14). The well characterized crystal ofx=0.11 (T _c=34.5 K) with nearly complete flux exclusion exhibits spin freezing at 8K(T _f) with significant spin fluctuation up to 20 K. The onset of spin fluctuation andT _f decrease against increasingx towardsx=0.15, suggesting an existence of a magnetic phase boundary aroundx whereT _c becomes maximum.     

Minerals and aligned collagen fibrils in tilapia fish scales: structural analysis using dark-field and energy-filtered transmission electron microscopy and electron tomography

The mineralized structure of aligned collagen fibrils in a tilapia fish scale was investigated using transmission electron microscopy (TEM) techniques after a thin sample was prepared using aqueous techniques. Electron diffraction and electron energy loss spectroscopy data indicated that a mineralized internal layer consisting of aligned collagen fibrils contains hydroxyapatite crystals. Bright-field imaging, dark-field imaging, and energy-filtered TEM showed that the hydroxyapatite was mainly distributed in the hole zones of the aligned collagen fibrils structure, while needle-like materials composed of calcium compounds including hydroxyapatite existed in the mineralized internal layer. Dark-field imaging and three-dimensional observation using electron tomography revealed that hydroxyapatite and needle-like materials were mainly found in the matrix between the collagen fibrils. It was observed that hydroxyapatite and needle-like materials were preferentially distributed on the surface of the hole zones in the aligned collagen fibrils structure and in the matrix between the collagen fibrils in the mineralized internal layer of the scale.     

Solution-phase total synthesis of the hydrophilic natural product argifin using 3,4,5-tris(octadecyloxy)benzyl tag

A solution-phase total synthesis of argifin using 3,4,5-tris(octadecyloxy)benzyl tag as a hydrophobic protective group of carboxylic acid was developed to produce 44% overall yield for 16 linear steps. Argifin, a novel class of natural product chitinase inhibitor, is a highly water-soluble cyclic pentapeptide, so hitherto, only solid-phase synthesis techniques have been used to conveniently prepare the compound and its derivatives. 3,4,5-Tris(octadecyloxy)benzyl alcohol (HO-TAGa) and its esters are highly crystalline materials and highly capable of dissolving in less-polar solvents such as dichloromethane, benzene, THF, etc., but insoluble in polar solvents such as methanol and DMSO. The combination of HO-TAGa and Fmoc-based peptide synthesis, together with simple purification by recrystallization from MeOH solution, furnished an efficient and practical route of argifin production in the liquid-phase.     

Sliding behavior of water droplets on line-patterned hydrophobic surfaces

We prepared line-patterned hydrophobic surfaces using fluoroalkylsilane (FAS) and octadecyltrimethoxysilane (ODS) then investigated the effect of line direction on sliding behavior of water droplets by direct observation of the actual droplet motion during sliding. Water droplets slide down with a periodic large deformation of the contact line and sliding velocity fluctuation that occurred when they crossed over the 500-μm ODS line regions in FAS regions on a Si surface tilted at 35°. These behaviors are less marked for motion on a 100-μm line surface, or on lines oriented parallel to the slope direction. Smaller droplets slide down with greater displacement in the line direction on 500-μm line patterning when the lines were rotated at 13° in-plane for the slope direction. This sliding behavior depended on the droplet size and rotation angle, and is accountable by the balance between gravitational and retentive forces.     

Electrospinning of Chitosan

Summary: An electrospun nonwoven fabric of a cationic polysaccharide, chitosan, was successfully prepared. The present study focuses on the effect of the electrospinning solvent and the chitosan concentration on the morphology of the resulting nonwoven fabrics. The solvents tested were dilute hydrochloric acid, acetic acid, neat formic acid and trifluoroacetic acid. As the chitosan concentration was increased, the morphology of the deposition on the collector changed from spherical beads to interconnected fibrous networks. The addition of dichloromethane to the chitosan‐TFA solution improved the homogeneity of the electrospun chitosan fiber. Under optimized conditions, homogenous (not interconnected) chitosan fibers with a mean diameter of 330 nm were prepared.

Effects of the coexisting dichloromethane (MC) in the prespun chitosan‐TFA solution on the morphology of the electrospun chitosan fibers. The volume ratio of TFA:MC was 70:30 (×5 000).     

Photoresponsive Peptide and Polypeptide Systems, 14. Biodegradation of Photocrosslinkable Copolypeptide Hydrogels Containing L‐Ornithine and δ‐7‐Coumaryloxyacetyl‐L‐ornithine Residues

Copoly[Orn/Orn(Cou)] containing δ‐7‐coumaryloxyacetyl‐L ‐ornithine [Orn(Cou)] and L ‐ornithine (Orn) residues was synthesized by the N‐carboxyanhydride method. When aqueous solutions of copoly[Orn/Orn(Cou)] containing 5–10 mol‐% of Orn(Cou) are irradiated, the photoinduced dimerization reaction between coumarin moieties in the side chains proceeds slowly, and after 24 h the solutions become transparent hydrogels. The gels exhibit solvent‐induced reversible expansion and contraction behavior in both water and ethanol. The biodegradation of the hydrogels by proteolytic enzymes and soil filamentous fungi is investigated using photocrosslinked copoly[Orn/Orn(Cou)] gels. The copoly[Orn⁸⁹/Orn(Cou)¹¹] gel is degradable by protease type XXIII, but not by trypsin. In the biochemical oxygen demand test, the order of the microbial biodegradation (%) was Rhizopus sp. (92%) > A. oryzae (38%) > P. caseicolum (18%) > P. citrinum (11%) > Cladosporium sp. (6%). The order for the copoly[Orn⁸⁹/Orn(Cou)¹¹] hydrogel is inverse to that for a polylysine/glutaraldehyde gel. These results suggest that the biodegradabilities of photocrosslinked hydrogels can be controlled by the monomer ratio of Orn, Orn(Cou) and lysine (Lys) in the parent copoly(amino acid)s of the photocrosslinked hydrogels.     

Reversible 1,3‐dipolar cycloaddition of dimethyl 2‐thiono‐1,3‐dithiole‐4,5‐dicarboxylate with dimethyl acetylenedicarboxylate

It was shown that dimethyl 2‐thiono‐1,3‐dithiole‐4,5‐dicarboxylate ( 2 ) and dimethyl acetylenedicarboxylate (DMAD) undergo a 1,3‐dipolar cycloaddition to produce a short‐lived ylide intermediate ( 3 ). The 1,3‐dipolar cycloaddition took place even at room temperature, although sluggishly, but took place much more rapidly under application of a high pressure of 500 MPa. The 1,3‐dipolar cycloaddition is reversible and the ylide 3 immediately splits into 2 and DMAD. When the reaction of 2 with DMAD was carried out at room temperature without solvent, a spiro‐1,3‐dithiole ( 11 ) was formed in 11% yield, whereas the reaction at 150°C provided a thiophene derivative ( 13 ) in 41% yield. It was found that 11 undergoes a thermal rearrangement to 13 . Results of attempted chemical trapping of the ylide 3 are also reported. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:434–440, 2000     

Formation of Giant Needle‐Like Polycation‐Bile Acid Complexes

The complexation of bile acids with various solvated polycations was studied. A one‐to‐one complex was precipitated when an aqueous solution of cholic acid sodium salt (CA) was mixed with aqueous solutions of 3,3‐ionene and grew to form crystals with needle‐like morphology, 3 millimeters in length. Hydrogen bonding of hydroxyls at the steroid face and the spacing between cationic sites of polycations were crucial for the formation of the giant needle.

Crossed polarizing microscopic photograph of the complex composed of cholic acid sodium salt and 3,3‐ionene.