Total synthesis of kehokorins A and B

The total synthesis of a dibenzofuran rhamnoside, kehokorin A, and its aglycone, kehokorin B, was achieved via a route including Suzuki-Miyaura cross-coupling followed by Ullmann ether synthesis to form a dibenzofuran, stepwise bromination at C7 of the dibenzofuran, a second Suzuki-Miyaura cross-coupling to install a 4-methoxyphenyl group at C7, and rhamnosylation.     

Storage and retrieval of a squeezed vacuum

Storage and retrieval of a squeezed vacuum was successfully demonstrated using electromagnetically induced transparency. The squeezed vacuum pulse having a temporal width of 930 ns was incident on the laser cooled 87Rb atoms with an intense control light in a coherent state. When the squeezed vacuum pulse was slowed and spatially compressed in the cold atoms, the control light was switched off. After 3 mus of storage, the control light was switched on again, and the squeezed vacuum was retrieved, as was confirmed using the time-domain homodyne method.     

Source breakup dynamics in Au + Au collisions at sqrt[s(NN)]=200 GeV via three-dimensional two-pion source imaging

A three-dimensional correlation function obtained from midrapidity, low p(T), pion pairs in central Au+Au collisions at sqrt[s(NN)]=200 GeV is studied. The extracted model-independent source function indicates a long range tail in the directions of the pion pair transverse momentum (out) and the beam (long). A proper breakup time tau(0) ~ 9 fm/c and a mean proper emission duration Delta tau ~ 2 fm/c, leading to sizable emission time differences ({|Delta t(LCM)|} approximately 12 fm/c), are required to allow models to be successfully matched to these tails. The model comparisons also suggest an outside-in "burning" of the emission source reminiscent of many hydrodynamical models.     

Crystal structure of a ten-amino acid protein

What is the smallest protein? This is actually not such a simple question to answer, because there is no established consensus among scientists as to the definition of a protein. We describe here a designed molecule consisting of only 10 amino acids. Despite its small size, its essential characteristics, revealed by its crystal structure, solution structure, thermal stability, free energy surface, and folding pathway network, are consistent with the properties of natural proteins. The existence of this kind of molecule deepens our understanding of proteins and impels us to define an "ideal protein" without inquiring whether the molecule actually occurs in nature.     

Syntheses, crystal and solution structures, ligand-exchange, and ligand-coupling reactions of mixed pentaarylantimony compounds

All possible combinations of mixed pentaarylantimony compounds bearing p-methylphenyl and p-trifluoromethylphenyl groups were synthesized; ArnTol5-nSb (n=0-5: Ar=p-CF3C6H4, Tol=p-CH3C6H4): Tol5Sb (1), ArTol4Sb (2), Ar2Tol3Sb (3), Ar3Tol2Sb (4), Ar4TolSb (5), and Ar5Sb (6). Compounds 2-5 are the first well-characterized examples of mixed acyclic pentaarylantimony species. The structures of 2-6 were determined by X-ray crystallography to feature trigonal-bipyramidal (TBP) geometry with the more electronegative p-trifluoromethylphenyl substituents selectively occupying the apical positions. Consideration of the chemical shifts of the ipso carbons of the aryl and tolyl groups suggested that the solution structures of 1-6 were also TBP, although their pseudorotation could not be frozen even at -80 degrees C. Ligand-exchange reactions (LERs) took place between 1 and 6 at approximately 60 degrees C in [D6]benzene and all six species 1-6 were found in the equilibrium mixture. The relative stabilities of 1-6 were determined quantitatively by comparison of the observed molar ratios of 1-6 in equilibrium with calculated statistical molar ratios, and Ar2Tol3Sb (3) was found to be the most stable. The ligand-coupling reactions (LCRs) of 2-5 in solution were greatly accelerated by adding Cu(acac)2 or Li+TFPB- (TFPB: [3,5-(CF3)2 C6H3]4 B), whereby the rate becomes comparable to the LER. The use of flash vacuum thermolysis (FVT) allowed the LCR to occur with very little ligand-exchange; the exception ArTol4Sb had very fast ligand-exchange. The selectivities of the LCRs were calculated from the yield of the biaryls synthesized by using FVT. These results were highly consistent with reactions catalyzed in solution, in which bitolyl was not obtained at all. The experimental results suggested that the LCR of pentaarylantimony compounds proceeds in the manner of apical-apical coupling.     

Synthesis and x‐ray crystal structures of hypervalent hexacoordinate antimony compounds without halogen ligands

Hypervalent hexacoordinate antimony‐ate complex { 2‐Et₄N : Rf₃Sb⁻Et₄N⁺ (Rf: o‐C₆H₄C(CF₃)₂O‐)} was synthesized by the reaction of Rf₂SbCl with lithium 1,1,1,3,3,3‐hexafluoro‐2‐(2‐lithiophenyl)‐2‐propoxide followed by countercation exchange. Reaction of 2‐Et₄N with triethyloxonium tetrafluoroborate gave the O‐ethylated adduct ( 3 ). X‐ray crystallographic analysis of 2‐Et₄N and 3 showed distorted octahedral structures of these compounds. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:33–37, 2001     

Ring-forming reaction via regioselective intramolecular insertion by (phenylthio) carbene into α c-h bond of alkoxides

ω-(Phenylthio)-ω-chloroalkyl acetates were allowed to react with MeLi (3.2 equiv) to give 2-(phenylthio) cycloalkanols which were produced by the regioselective intramolecular insertion by (phenylthio) carbenes.     

High-Contrast Imaging of Nano-Channels Using Reflection Near-Field Scanning Optical Microscope Enhanced by Optical Interference

We demonstrated a contrast enhancement in a near-field scanning optical microscope (NSOM) by optical interference with an aperture probe in reflection (illumination-collection) mode operation. We observed a NiO film deposited on a sapphire substrate and clearly visualized 2-nm-deep nano-channel structures on the surface of the film. The reflection NSOM enhanced by optical interference is quite a promising instrument for high-resolution optical detection and estimation of low-contrast nanostructures.     

A SOGICON type instability in silicon

A current oscillation phenomenon in SOGICON type Si device fabricated by the use of a planar process is studied. The oscillation is generated in the region between anode and notch which is located at the center on the sample. A considerably high electric field is observed in the notch region. Considering the hot-electron effect due to the high electric field, the mechanism underlying the current oscillation is discussed.     

Finite-temperature effect on broken UA(1) symmetry and the η′ mass

The U_A(1) symmetry-breaking effective lagrangian mediated by the instanton is calculated in the semiclassical approximation at finite temperature. It is found that the strength of the effective vertex decreases with increasing temperature up to the QCD scale. Also, we discuss the possible variation of the η′ and other pseudoscalar meson masses.