L-DMDP, L-homoDMDP and their C-3 fluorinated derivatives: synthesis and glycosidase-inhibition

L-DMDP and L-homoDMDP, the enantiomers of naturally occurring DMDP and homoDMDP have been synthesized from D-xylose derived cyclic nitrone 9. Their 3-deoxy-3-fluorinated analogues were also obtained from polyhydroxylated fluorinated cyclic nitrone 10, which was prepared from fluorinated sugar 12 in seven steps. Bioactivities of these iminosugars against various glycosidases were evaluated. While L-DMDP and L-homoDMDP are potent inhibitors of α-glucosidases, a sharp decrease of inhibition was found when the C-3 hydroxyl group of these compounds was replaced by fluoride, which showed the great importance of the C-3 hydroxyl in their interaction with enzymes.     

Role of base in the formation of silver nanoparticles synthesized using sodium acrylate as a dual reducing and encapsulating agent

The formation mechanism of Ag nanoparticles (NPs) synthesized with a wet-chemical reduction method using sodium acrylate as a dual reducing and capping agent was investigated with various analytical techniques. The time course of the state of the reaction solution was investigated using UV-vis and XAFS spectroscopies which showed that the NP formation rate increased with increasing concentration of sodium hydroxide (NaOH). The detailed kinetic analyses reveal that both the reduction rate of Ag ions and the nucleation rate of Ag NPs are dramatically increased with increasing NaOH concentration. XANES analyses imply that another reaction pathway via alternative Ag(+) species, such as Ag(OH)(x), was developed in the presence of NaOH. Consequently, NaOH is found to play an important role not only in creating specific intermediates in the reduction of Ag(+) to Ag(0), but also in accelerating the reduction and nucleation rates by enhancing the oxidation of sodium acrylate, thereby increasing the rate of formation of the Ag NPs.     

Optical and electronic properties of siloxane-bridged cyclic dimers with naphthylene or pyrenylene moieties

The optical and electronic properties of novel siloxane-bridged cyclic dimers with naphthylene (CD1) or pyrenylene (CD2) moieties are described. CD1 and CD2 were obtained by the cyclic dimerization of 1,4-bis(dimethylhydroxysilyl)naphthalene (M1) and 1,6-bis(dimethylhydroxysilyl)pyrene (M2), respectively. CD1 and CD2 mainly exhibited the emission from their excimers owing to their short distances between aryl moieties in CD1 and CD2, which were determined to be 3.44 Å and 3.41 Å by the X-ray crystallographic analysis, respectively. The absorption spectra of CD2 in the presence of 7,7,8,8-tetracyanoquinodimethane (TCNQ) revealed that CD2 has the ability to form 1:1 charge-transfer complex with TCNQ, indicating the existence of the transannular π-π interaction between closely located pyrene components in CD2.     

Synthesis of the putative structure of fistulosin using the ruthenium-catalyzed cycloisomerization of diene

Fistulosin 1, which was isolated from the root of the Welsh onion, is a novel indole alkaloid that has antifungal activity. The first total synthesis of the reported structure of fistulosin using our cycloisomerization of diene is described.     

Environment-dependent ultrafast photoisomerization dynamics in azo dye

Azoaromatic dyes have been extensively investigated over the past decade due to their potential use in a variety of optical devices that exploit their ultrafast photoisomerization processes. Among the azoaromatic dyes, Disperse Red 19 is a commercially available azobenzene nonlinear optical chromophore with a relatively high ground-state dipole moment. In the present study, we used ultrafast time-resolved spectroscopy to clarify the dynamics of a push-pull substituted azobenzene dye. Solution and film samples exhibited different ultrafast dynamics, indicating that the molecular environment affects the photoisomerization dynamics of the dye.     

Preparation of low-surface-energy poly[2-(perfluorooctyl)ethyl acrylate] microparticles and its application to liquid marble formation

We demonstrate the successful preparation of stable liquid marbles from various liquids. This is accomplished by using low-surface-energy poly[2-(perfluorooctyl)ethyl acrylate] (PFA-C(8)) as microparticles. The PFA-C(8) microparticles were prepared by the spontaneous self-organized microparticulation of PFA-C(8). The physical properties remained intact in the polymer morphology as confirmed by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) measurements. The extremely low surface energy of PFA-C(8) provides a high solid-liquid spreading coefficient (S(S/L)) value for various combinations of liquids. As a result, liquid marbles were obtained from various liquids, unlike the case with other fluorine polymer particles such as poly(tetrafluoroethylene) (PTFE) and poly(vinilydene fluoride) (PVDF). These results suggest that the technique is widely applicable for preparing novel functional materials.     

Water flow in poly(N-isopropylacrylamide) gels

Friction between a polymer network of poly(N-isopropylacrylamide) gels and solvent water was investigated. The gel was mechanically constrained in a glass capillary at gelation, and hydrostatic pressure was directly applied to the cross section of the cylinder. The temperature dependence of the flow velocity was extensively measured in the vicinity of the transition temperature for gels with different lengths, l(0), at gelation. As the temperature increased, the friction slightly decreased at the transition point and increased rapidly in the collapsed phase. Although the flow velocity depended on l(0), the friction in the vicinity of the transition point was well scaled by l(0) based on the Hagen-Poiseuille equation for the flux of water flow in a capillary. The results suggested that the assumption that the gel is a bundle of microcapillaries was applicable to the water flow through the hydrogel, which was largely deformed not only by the pressure applied to the solvent but also by the shrinking force caused by the temperature increment. Macroscopic deformation did not affect the friction between the three-dimensional polymer network and water.     

A regio- and stereoselective alpha-methylation of gamma,delta-epoxy-alpha,beta-unsaturated esters with a Me2Zn-CuCN reagent

A highly regio- and stereoselective alpha-methylation reaction of gamma,delta-epoxy-alpha,beta-unsaturated esters was achieved by using a Me2Zn-CuCN reagent.