Preparation of graphene oxide-coated silk fibers through HBPAA [a molecular glue]-induced layer-by-layer self-assembly

Carbon nanomaterials recently gained extensive interests for their good application potential in composite nanomaterials because of their unique physicochemical properties. In this study, graphene oxide (GO)-coated silk fibers were fabricated through HBPAA-induced layer-by-layer (LbL) self-assembly technology. The closely adhered GOs coatings were achieved by circular incubation with solutions of hyperbranched poly (amidoamine) (HBPAA) and GOs, with HBPAA serving as the “molecular glue” that could bind single or mutilayered GOs to the surface of silk fibers. In the experiments, GOs nanosheets were synthesized by a modified Hummers method and were characterized by atomic force microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Our developed technology was able to tightly bind GOs to the silk surface and control their loading capacity. Owing to the positive charges and abundant amino end groups of HBPAA, GOs were found to be completely adsorbed onto silk surface. Therefore, their assembly would be green and controllable. The Fourier transform infrared (FTIR) spectroscopy, XPS, XRD, Thermogravimetric analyses (TGA) confirmed the attachment of HBPAA and GOs. Field mission scanning electron microscopy (FESEM) indicated that GOs closely spread on the surface of silk fibers without any self-folding though excessive stacking were observed in a small part of a silk surface with the increased density of GOs coatings. The developed LbL self-assembly technology may provide a controllable approach to coat GOs on the surface of biological fibers and graphene-based functional materials.     

A sequential highly stereoselective hydroboration and Suzuki-Miyaura cross-coupling reaction of fluoroalkylated internal acetylenes: a practical one-pot synthesis of fluoroalkylated trisubstituted alkenes

The one-pot synthesis of trisubstituted alkenes starting from fluoroalkylated internal alkynes was investigated. Hydroboration of the alkynes proceeded in a highly regio- and stereoselective manner to give the corresponding vinylboranes in excellent yields. Without isolation, treatment of the vinylboranes with various aryl halides under the Suzuki-Miyaura cross-coupling conditions gave the fluoroalkylated trisubstituted alkenes in high yields with complete retention of the olefinic geometry.     

Highly diastereoselective reductive coupling of 2-bromo-2,3,3,3-tetrafluoropropanamide with aldehydes promoted by triphenylphosphine-titanium(IV) isopropoxide. An efficient route to the synthesis of erythro-alpha-fluoro-alpha-(trifluoromethyl)-beta-hydroxy amides

The reductive coupling reaction of N-methoxy-N-methyl-2-bromo-2,3,3,3-tetrafluoropropanamide (Weinreb amide) with various aldehydes under the influence of the combined reagent, 1.2 equiv each of triphenylphosphine and titanium(IV) isopropoxide, took place smoothly at ambient temperature to give the corresponding alpha-fluoro-alpha-(trifluoromethyl)-beta-hydroxy amides in a highly erythro-selective manner. The high erythro selectivity was also obtained even by employing a combination of triphenylphosphine (1.2 equiv) and a catalytic amount of titanium(IV) isopropoxide.     

Highly self-organized electron transfer from an iridium complex to p-benzoquinone due to formation of a pi-dimer radical anion complex triply bridged by scandium ions

Unusually high kinetic order was observed in self-organized Sc3+-promoted electron transfer from tris(2-phenylpyridine)iridium(III) [Ir(ppy)3] to p-benzoquinone (Q) in propionitrile, third-order with respect to the concentration of Sc3+ and second-order with respect to the concentration of Q, to produce a pi-dimer semiquinone radical anion complex that is triply bridged by three Sc3+ ions (Q*--3Sc3+-Q).     

Experimental evidence for intramolecular blue-shifting C-H...O hydrogen bonding by matrix-isolation infrared spectroscopy

Experimental evidence for intramolecular blue-shifting C-H...O hydrogen bonding is presented. Argon matrix-isolation infrared spectra of 1-methoxy-2-(dimethylamino)ethane exhibit a band at 3016.5 cm-1. Spectral behavior with annealing indicates that this band is assigned to the most stable conformer, trans-gauche-(trans|gauche'), with an intramolecular C-H...O hydrogen bond. Density functional calculations show that this band arises from the stretching vibration of the C-H bond participating in the formation of the C-H...O hydrogen bond. The C-H bond is shortened by 0.004 A, and the C-H stretching band is blue-shifted by at least 35 cm-1 on the formation of the hydrogen bond. The (C)H...O distance is calculated as 2.38 A, which is shorter than the corresponding van der Waals separation by 0.3 A.     

Reaction of β-trifluoroethoxy vinamidinium salts with carbon nucleophiles

β-Trifluoroethoxy vinamidinium salts 1 reacted smoothly with various types of the carbanions, generated by treatment of ketones, esters, amide and nitriles with LDA, to give the corresponding trifluoroethoxylated multifunctional dienamine derivatives 3 in moderate to good yields. On the other hand, the reaction of 1 with lithium acetylide and other carbanions derived from methyl compounds bearing sulfonyl, sulfinyl, and phosphonyl groups produced the corresponding α,β-unsaturated aldehydes 5 in good yields.     

Remarkable effects of counter ions on scandium ion-promoted electron transfer reactions

Scandium ion-promoted electron transfer reactions of p-benzoquinone are remarkably accelerated when tetrakis(pentafluorophenyl)borate anion is used instead of trifluoromethanesulfonate anion as the counter anion of scandium ion. Only a catalytic amount of scandium borate salt (Sc[B(C6F5)4]3) accelerates significantly the Diels-Alder reaction of 9,10-dimethylanthracene with p-benzoquinone, which proceeds via Sc(3+)-promoted electron transfer from the anthracene to p-benzoquinone.     

Synthesis and structural revision of eurypamides isolated from the Palauan sponge Microciona eurypa

Eurypamides A and B, 1 and 2, were successfully synthesized by employing Tl(NO₃)₃ (TTN) oxidation of the corresponding halogenated phenols, 9, 16, and 26. This investigation revealed that the dihydroxyarginine residue of 1 should be revised to possess (2S,3R,4S)-configuration. In addition, the synthesis of 2 provided a pure sample, which was previously characterized in a mixture.     

Complete reversal in regioselectivity in the Baeyer-Villiger reaction of an alpha-CF(3)-ketone and theoretical rationale for axial orientation of sterically demanding CF(3) group at the transition state

The regioselectivity of the Baeyer-Villiger reaction of alpha-CF(3)-ketone is completely reversed from that in alpha-F(eq)-ketone. Theoretical study rationalized that the reaction proceeds with the sterically demanding CF(3) group in an axial orientation by strong dipole interaction. The guiding principle that strong dipole interaction can overcome steric repulsion as a determining factor not only in regio- but also in stereocontrol is proposed. [reaction: see text]     

Encapsulation‐Induced Remarkable Stability of a Hydrogen‐Bonded Heterocapsule

Remarkably enhanced stability of the self‐assembled hydrogen‐bonded heterocapsule 1?2 by the encapsulation of 1,4‐bis(1‐propynyl)benzene 3 a was found with K_a=1.14×10⁹ M ^?1 in CDCl₃ and K_a2=1.59×10⁸ M ^?2 in CD₃OD/CDCl₃ (10 % v/v) at 298 K. The formation of 3 a @( 1?2 ) was enthalpically driven (ΔH°<0 and ΔS°<0) and there was a unique inflection point in the correlation between ΔH° versus ΔS° as a function of polar solvent content. The ab initio calculations revealed that favorable guest–capsule dispersion and electrostatic interactions between the acetylenic parts (triple bonds) of 3 a and the aromatic inner space of 1?2 , as well as less structural deformation of 1?2 upon encapsulation of 3 a , play important roles in the remarkable stability of 3 a @( 1?2 ).