Remote Control of One-Handed Helicity in Polyacetylenes through Flexible Spacers in Water: Impact of the Spacer Length

We report the unprecedented sergeants and soldiers (S&S)-type remote control of one-handed helicity in copolymers of chiral/achiral biphenylylacetylenes bearing amphiphilic oligo(ethylene glycol) (OEG) side chains. A small amount of chiral binaphthyl residues (≤10 mol %) introduced at the terminal of the achiral OEG spacers as many as 80 bonds away from the polymer backbones induced a complete one-handed helix in water through preferential intramolecular encapsulation of the binaphthyl groups within a cavity of the copolymers. A fully one-handed helix can be induced virtually independent of the OEG spacer length and concentrations. At a specific spacer length, however, its helix-sense was inverted. The copolymers also form an excess one-handed helix in organic solvents in an OEG spacer-length dependent manner, yet far from the polymer backbones. We show the superiority of the present covalent-bond driven S&S-type remote helicity control over the corresponding noncovalent helicity induction approach.     

HRTEM image contrast of short range order in Ni4Mo

The high resolution transmission electron microscope (HRTEM) imaging of short range order (SRO) in Ni4Mo was investigated by means of multi-slice image simulations. The HRTEM images of Ni4Mo exhibit locally bright dot patterns corresponding to the [001] projections of the N2M2-type (chalcopyrite-like) structure. The multi-slice simulations revealed that the N2M2 patterns are rationalized as the projection patterns of the SRO structure which consists of subunit cell clusters of D1a, D022 and Pt2Mo structures. The N2M2-type image contrast appears when both the fundamental fcc lattice reflections and the 1 1/2 0 diffuse scattering of SRO contribute enough to imaging. This suggests that a good coincidence in intensity distribution between the Fourier power spectra of HRTEM images and the electron diffraction patterns is one of the conditions for the image contrast of SRO to be interpreted in terms of the projection contrast.     

Flow characteristics around a square cylinder with changing chamfer dimensions

Abstract  

It is known that for a square cylinder subjected to uniform flow, the drag force changes with the angle of attack. To clarify the flow characteristics around a square cylinder with corner cutoffs, we measured the drag coefficient and the Strouhal number for changing chamfer dimensions. We analyzed the flow around a square cylinder with corner cutoffs by applying the RNG k–ε turbulent model, and investigated the surface flow pattern using visualization by means of the oil film and mist flow method. From these results, we obtained the surface flow patterns by the oil film method and numerical analysis. The numerical results agreed well with the experimental values. The drag coefficient of the square cylinder with corner cutoffs decreased suddenly at an angle of attack of about α = 0°– 10° when compared with the drag coefficient for a square cylinder. The minimum value of the drag coefficient for the square cylinder with corner cutoffs decreased by about 30% compared with that for the square cylinder. The drag coefficient of the square cylinder with 10% corner cutoffs was found to be smallest, since the wake area of this square cylinder was smaller compared with that of the other square cylinder.     

Energy Transfer‐Assisted Whispering Gallery Mode Lasing in Conjugated Polymer/Europium Hybrid Microsphere Resonators

Lanthanide metal complexes display luminescence with narrow bandwidth. Here, we present coupling of the luminescence from europium ion (Eu³⁺) with whispering gallery modes (WGMs) in conjugated polymer microsphere resonators. Self‐assembly of fluorene–terpyridine alternating copolymer, coordinated by Eu³⁺ (F8tpy‐Eu³⁺), forms well‐defined microspheres with an average diameter of 3.2 μm. Upon focused laser excitation, a microsphere of F8tpy copolymer displays WGM photoluminescence (PL) at a wide spectral range from 420 to 680 nm. In contrast, F8tpy‐Eu³⁺ hybrid microspheres exhibit sharp WGM PL at a narrow spectral range of 615–630 nm, which is characteristic of luminescence from Eu³⁺. The PL behavior indicates that photoinduced energy transfer from F8tpy to Eu³⁺ occurs efficiently. Furthermore, the intensity of the PL peak increases nonlinearly upon strong pumping, indicating that a lasing action appears with the threshold of 1.85 mJ cm^?2. These results will pave the way for developing microlasers and photonic devices from soft organic materials.     

Ethylene hydrogenation on Ni(1 0 0) surface

The hydrogenation of ethylene on Ni(1 0 0) surface has been studied by TDS. The decrease in the bonding energy with increasing coverage is revealed for both of adsorbed hydrogen and ethylene by the shift of desorption to lower temperatures. Ethane formation is only observed on the preadsorbed hydrogen coverage exceeding 0.5 monolayer (ML), coupled with the growth of H₂ shoulder peak at lower temperatures. Further increase of H coverage to saturation reduces the bonding energy of subsequently adsorbed ethylene by 15 kJ/mol and decreases the saturation coverage of ethylene to about one-third on the clean surface. This leads to the shift of ethane desorption from 250 to 220 K and an appearance of additional ethane peak at 180 K. The latter ethane formation coincides with the hydrogenation of surface ethyl species derived from ethyl iodide as a precursor. It indicates that the rate of ethyl formation on the surface would be comparable to that of subsequent hydrogen addition to the surface ethyl species in the hydrogenation of ethylene when the preadsorbed hydrogen coverage approaches 1.0 ML.     

Preparation and antitumor activity of 2'-O-, 3'-O- and 2',3'-di-O-substituted derivatives of etoposide.

The 2'-O-, 3'-O- and 2',3'-di-O-substituted derivatives (4a--p) of etoposide were prepared by nucleophilic substitution of 4'-O-benzyloxycarbonyletoposide (2) followed by deprotection. Controlled reaction (a limited amount of reagents and low temperature) was required for preparing the mono-O-substituted derivatives. In terms of ED125 values, doses which show 125% of T/C against P388 leukemia in mice, both the 2'-O-acetate (4a, ED125 = 0.18 mg/kg) and 3'-O-acetate (4b, 0.23 mg/kg) were nearly as active as etoposide (1, 0.19 mg/kg), while the 2',3'-di-O-acetate (4c, 1.9 mg/kg) was somewhat less potent. In the replacement with other substituents, antitumor activity of the 2'-O-substituted derivatives was affected much more by the difference of the substituents as compared with that of the corresponding 3'-O-substituted derivatives. In the 2',3'-di-O-substituted derivatives, the activity was decreased additively on the substituents.     

Degradation and isomerization of 1,2-dichloroethenes by photocatalytic reactions

The photocatalytic degradation and isomerization of trans- and cis-1,2-dichloroethenes (1,2-DCEs) by TiO₂ photocatalyst have been investigated using gas chromatography. The reaction half-life of 1,2-DCEs in nitrogen was longer than in dry air and oxygen, and the initial concentration of them affects the extent of the isomerization. The results indicate that the oxygen molecule and chlorine atoms play an important role in the degradation and isomerization of 1,2-DCE. It is also apparent that the photocatalytic degradation of 1,2-DCEs occurs on the TiO₂ surface.     

Monomeric copper(II) and nickel(II) complexes of N,N,N′,N′-tetrakis [(2-benzimidazolyl)methyl]-1,2-cyclohexanediamine], a chelating ligand containing imidazole groups

Summary Cu^II and Ni^II coordination compounds with N,N,N,N-tetrakis[(2-benzimidazolyl)methyl]-1,2-cyclohexanediamine (CDTB) have been prepared and characterized. The crystal structure of [Cu(CDTB)](ClO₄)₂ has been determined. The geometry around the Cu atom is highly irregular and can best be described as a cis-distorted octahedron, with four short CuN bond distances of 1.988(3) Å and 2.028(3) Å, and two very long CuN bond lengths of 2.543(4) A. The cis NCuN chelate angles in the complex range from 68.8(2) for N(1)CuN(1) to 141.03° for N(4)CuN(1). The cyclic voltammogram of the complex shows a fully reversible one-electron redox wave at E _1/2 = 0.162V versus standard calomel electrode, corresponding to the Cu^I/II redox couple. The structure of [Ni(CDTB)](NO₃)₂ ·EtOH has also been determined. The geometry around the Ni atom in this compound can be described as distorted octahedral, with N(4), N(4), N(1), N(1) as the ligating atoms in the basal plane, with cis chelate angles ranging from 79.37(10) to 120.9(2)° with the trans N(2)NiN(2) angle at 175.1(2)°. The structural differences in these two compounds are undoubtedly electronic rather than steric.