Highly Efficient Dehydrogenative Coupling of Hydrosilanes with Amines or Amides Using Supported Gold Nanoparticles

Hydroxyapatite‐supported gold nanoparticles (Au/HAP) can act as a highly active and reusable catalyst for the coupling of hydrosilanes with amines under mild conditions. Various silylamines can be selectively obtained from diverse combinations of equimolar amounts of hydrosilanes with amines including less reactive bulky hydrosilanes. This study also highlights the applicability of Au/HAP to the selective synthesis of silylamides through the coupling of hydrosilanes with amides, demonstrating the first example of an efficient heterogeneous catalyst. Moreover, Au/HAP shows high reusability and applicability for gram‐scale synthesis.     

Formation of Supramolecular Nanostructures through in Situ Self-Assembly and Post-Assembly Modification of a Biocatalytically Constructed Dipeptide Hydrazide**

Aqueous self-assembly of short peptides has attracted growing attention for the construction of supramolecular materials for various bioapplications. Herein, we describe how the thermolysin-assisted biocatalytic construction of a dipeptide hydrazide from an N-protected amino acid and an amino acid hydrazide leads to the formation of thermally stable supramolecular hydrogels. In addition, we demonstrate the post-assembly modification of the supramolecular architectures constructed in situ tethering hydrazide groups as a chemical handle by means of fluorescence imaging.     

A new aliphatic ester of hydroxysalicylic acid from fermented Carica papaya L. preparation with a potential hair growth stimulating activity

Abstract

An aliphatic ester of hydroxysalicylic acid (6), reported for the first time from a natural source in addition to five known compounds were isolated from the fermented Carica papaya L. preparation, a commercialized functional food. The known compounds were identified as 5-hydroxymethylfurfuraldehyde (1), trans-caffeic acid (2), butyl 4-hydroxybenzoate (butylparaben) (3), lycopene (4), benzyl isothiocyanate (5). Compounds 1 and 3 were reported for the first time from Papaya fruits through this study. The new compound showed a moderate antioxidant activity and a potent hair growth stimulating activity in vitro.     

Phase structure change and ER effect in liquid crystalline polymer/dimethylsiloxane blends

The mechanism of the electrorheological (ER) effect in two types of liquid crystalline polymer (LCP)/dimethylsiloxane (DMS) blends was investigated by rheological measurements and by structure observation under electric field and shear flow. The results show that the phase structures of these immiscible blends can be categorized into slipping (low viscosity) and non-slipping (high viscosity) states. In the non-slipping state, higher viscosity LCP domains connect the electrodes. In the slipping state, on the other hand, LCP domains do not connect the electrodes and the shear is mainly confined in the lower viscosity DMS domains. The ER effect (electrically induced viscosity increase) originates from the electrically induced slipping to non-slipping transition. In one of the blends, the ER effect occurs only at high shear rate, since this blend is in non-slipping state even under no field if the shear rate is low. Received: 29 April 1997 Accepted: 3 November 1997     

Optical switching and alignment of antiferroelectric liquid crystals containing an azo group

The optical properties of two kinds of photochromic antiferroelectric liquid crystal (AFLC) containing an azo group have been examined. Depending on the substituting group at the chiral centre, these AFLCs showed different photoinduced phase transitions by Ar⁺ laser light irradiation. This phase transition has led to a new form of optical switching controlled by a bias voltage. In addition, it was found that these AFLCs caused an azimuthal photoalignment effect regulated by linearly polarized Ar⁺ laser light irradiation. These phenomena were applied to image storage.     

D3h‐Symmetric Porphyrin‐Based Rigid Macrocyclic Ligands for Multicofacial Multinuclear Complexes in a One‐Nanometer‐Sized Cavity

The one‐step synthesis of D_3h‐symmetric cyclic porphyrin trimers 1 composed of three 2,2′‐[4,4′‐bis(methoxycarbonyl)]bipyridyl moieties and three porphyrinatozinc moieties was achieved from a nickel‐mediated reductive coupling of meso‐5,15‐bis(6‐chloro‐4‐methoxycarbonylpyrid‐2‐yl)porphyrinatozinc. Although cyclic trimers 1 were obtained as a mixture that included other cyclic and acyclic porphyrin oligomers, an extremely specific separation was observed only for cyclic trimers 1 when using columns of silica gel modified with pyrenylethyl, cyanopropyl, and other groups. Structural analysis of cyclic trimers 1 was carried out by means of NMR spectroscopy and X‐ray crystallography. Treatment of an η³‐allylpalladium complex with a cyclic trimer gave a tris(palladium) complex containing three η³‐allylpalladium groups inside the space, which indicated that the bipyridyl moieties inside the ring could work as bidentate metalloligands.     

Formal [6+4] cycloaddition of a dicobalt acetylene complex with furan derivatives

An efficient method for constructing a 10-membered carbocycle with an oxygen bridge has been developed on the basis of a formal [6+4] cycloaddition reaction. Under the influence of EtAlCl₂, a dicobalt hexacarbonyl acetylene complex possessing a benzoyloxy group and an allylsilane moiety reacted with furan to give a 11-oxabicyclo[6.2.1]undec-9-ene derivative. On treatment with iodine, the cycloadduct underwent decomplexation followed by rearrangement of the oxygen bridge to afford a 11-oxabicyclo[5.3.1]undeca-1,5-diene derivative.