Stereoselective synthesis of β-fluoroallyl alcohols

β-Fluoroallyl alcohols ($\text{6}$) were obtained with high stereoselectivity by the LiA1H₄ reduction of 1-acetoxy-3-alkyl-2,2-difluorocyclopropanes ($\text{5}$).     

Fe nanowire encapsulated in boron nitride nanotubes

Boron nitride (BN) nanotubes, nanohorns, nanocoils were synthesized by annealing Fe₄N and B powders at 1000 °C for 1 h in nitrogen gas atmosphere. Especially, Fe-filled BN nanotubes were produced, and investigated by high-resolution electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy, which indicates that the [110] of Fe is parallel to the BN nanotube axis. Formation mechanism of Fe-filled BN nanotube was speculated based on these results.     

A note on sign-solvability of linear system of equations

Given an n×(n+I) sign matrix (Ab). we are concerned with the condition that guarantees the solution to Ax=b be of a fixded sign pattern. It is shown that each factor of det (1) corresponds. in aone to one way to DM-component of the bipartite graph representation of A. This fact is used to supplement the proof of the graph-theoretic characterization of sign-solvability obtained by Bassett et al. [1] and subsequent authors.     

Visual enantiomeric recognition of amino acid derivatives in protic solvents

Various types of chiral host molecules 2-7 based on a phenolphthalein skeleton and two crown ethers were prepared for use in visual enantiomeric recognition, and we examined their enantioselective coloration in complexation with chiral amino acid derivatives 9-22 in methanol solution. Methyl-substituted host (S,S,S,S)-3 showed particularly prominent enantiomer selectivity for the alanine amide derivatives 11 and 12. A combination of methyl-substituted host (S,S,S,S)-3 with guest (R)-11 or (R)-12 developed a purple color, whereas no color development was observed with (S)-11 or (S)-12. On the other hand, phenyl-substituted host (S,S,S,S)-6 showed deeper coloration with a wide range of (S)-beta-amino alcohols compared to that seen with host (S,S,S,S)-6 and the corresponding (R)-beta-amino alcohols at 0 degrees C. Furthermore, absorbance inversion temperatures (AIT) were observed within the range of 0-50 degrees C in many cases.     

Characterization of the pH-dependent resonance Raman transitions of archaeal and bacterial Rieske [2Fe-2S] proteins

The pH-dependent resonance Raman (RR) spectral changes of the cytochrome bc1-associated, high-potential Rieske proteins have frequently been invoked to explain the redox-linked ionization behavior. We report herein RR spectral data of archaeal and bacterial Rieske proteins that directly demonstrate the pH-dependent changes near and above pKa,ox2, but not around pKa,ox1, of the visible circular dichroism (CD) transitions. The RR spectral changes are attributed to modification of the immediate [2Fe-2S] cluster environment due to deprotonation of some exchangeable amide groups in the polypeptide backbone, rather than previously assumed simple changes of the Fe-Nimid stretching vibrations.     

THE EFFECTS OF ULTRAVIOLET C ON in vitro NUCLEOSOME ASSEMBLY AND STABILITY

Abstract The effects of ultraviolet C (UVC) irradiation on nucleosome assembly and its stability were investigated quantitatively using an in vitro nucleosome assembly system comprising a plasmid DNA of pBR322 and core histones isolated from rat ascites hepatoma cells. Nucleosomal formation was estimated by analyzing the resulting DNA supercoils. When UVC-irradiated (3000 J/m²) DNA was used as a substrate for the nucleosome assembly system, the nucleosomal formation efficiency was reduced by half compared with nonirradiated DNA. On the other hand, when the reconstituted nucleosomes (minichromosomes) on the nonirradiated DNA were irradiated with UVC (3000 J/m²), about half each were disrupted and retained. These results indicate that it is difficult for UV-damaged DNA regions to supercoil around the histone octamers to form nucleosomes and that the histone octamers in the UV-damaged nucleosomes tend to be dissociated from DNA.     

Formation and structure of B24N24 clusters

Boron nitride (BN) nanocage clusters of B₂₄N₂₄ were synthesized and detected by laser desorption time-of-flight mass spectrometry. The B₂₄N₂₄ clusters consisted of 4-, 6- and 8-membered BN rings satisfying the isolated tetragonal rule, which was optimized by molecular orbital calculations. The electronic structure showed a bandgap energy of 4.9 eV, which is smaller than that of B₃₆N₃₆ cluster.