Optical-limiting property of cyclic phenylacetylene oligomer synthesized under high pressure

The optical-limiting property of a new cyclic phenylacetylene oligomer was investigated. Toluene solutions of the oligomer contained within a quartz cell were irradiated with the pulse from frequency doubled Nd: Yag laser at 532 nm. At low input fluence, the transmittance of the toluene solution was constant and agreed well with that obtained by spectrophotometer. At high input fluence, the transmittance of the solution above a concentration of 5 wt % decreased with input fluence. The oligomer had an optical limiting property. As the concentration of the oligomer increased from 5 to 20 wt %, the threshold for optical limiting decreased. The threshold was independent of the molecular weight. The optical limiting property was analyzed by the following equation obtained according to the reverse saturable absorption mechanism; log(I₀/I) = K(I₀ - I) + A_g, where I₀ is the input fluence, I is the output fluence, K is a parameter depending on the absorption cross section and the relaxation time, and A_g is the absorbance of the ground state. © 1996 John Wiley & Sons, Inc.     

Recent studies of unstable nuclei far from stability with the on-line isotope separators of JAERI

Studies on the decay of unstable nuclei using the two on-line isotope separators of JAERI are reviewed for the past five years. With the previously established ion-source technique using mono-oxide ion formation in a thermal ion source, the new nuclides¹²⁵Pr and¹²⁷Pr have been identified in heavy-ion fusion residues. Further, with a newly developed gas-jet coupled thermal ion source, the new nuclides¹⁶⁶Tb,¹⁶⁵Gd,¹⁶¹Sm and²³⁶Am have been identified by bombarding²³⁸U and²³⁵U targets with a proton or⁶Li beam. Other studies, including off-line experiments, by decay spectroscopy, laser spectroscopy and Mössbauer spectroscopy are described.     

Photooxygenation and photodimerization of 4-methoxystyrene in NaY. The role of co-adsorbed water and alkene–oxygen charge-transfer complex

On adsorption into NaY, 36% of 4-methoxystyrene (1) was consumed to yield its cis- and trans- chain dimers 2. Irradiation of the NaY sample under vacuum gave cyclic dimers 3, probably through the excimer of 1, and also caused trans-to-cis one-way isomerization of 2. When the NaY sample was irradiated under dry oxygen, 4-methoxybenzaldehyde (4) was given as the major product through photoinduced electron-transfer reaction on excitation of the contact charge-transfer complexes between the guest molecules and O₂. The effects of sodium ion and co-adsorbed water on the photodimerization and photooxygenation is also discussed.     

Ynolate chemistry. Reaction of a silylynolate with aziridines leading to gamma-lactams.

A silylynolate, generated via the carbonylation of lithium silyldiazomethane, was reacted with N-tosyl aziridines to produce various five-membered lactams in good yields. The key step of this reaction involves the ring-opening ketenylation of aziridines by the silylynolate. The reaction proceeded in a highly stereoselective manner, and ketenylation took place at the less hindered carbon. When treated with aldehydes prior to protonation, the alpha-silylated lactam enolates gave alpha-vinylidene gamma-lactams. These reactions represent a unique path to the generation of and for controlling the reactivity of a rare class of reactive intermediates, namely, acyllithium derivatives and ynolates.     

Design and synthesis of a dimeric derivative of RK-682 with increased inhibitory activity against VHR, a dual-specificity ERK phosphatase: implications for the molecular mechanism of the inhibition

BACKGROUND: VHR is a dual-specificity phosphatase, which dephosphorylates activated ERK1/2 and weakens the ERK signaling cascade in mammalian cells. A selective inhibitor is expected to be useful for revealing the physiological function of VHR. RESULTS: First, we investigated the molecular mechanism of VHR inhibition by a known natural product, RK-682. Kinetic analysis indicated that inhibition was competitive toward the substrate, and two molecules of RK-682 were required to inhibit one molecule of VHR. Based on the structure-activity relationships for VHR inhibition by RK-682 derivatives, we constructed a binding model using molecular dynamics calculation. Based on this model, we designed and synthesized a novel dimeric derivative. As expected, the dimeric derivative showed increased inhibition of VHR, supporting our proposed mechanism of VHR inhibition by RK-682. CONCLUSION: We have developed a novel inhibitor of VHR based on the results of kinetic analysis and docking simulation.     

Dimensional Crossover of Magnetic Transition in Diluted Ising Spin Nets Probed by Muon Spin Relaxation

The magnetic ordering process of Ising spins on diluted square lattice was studied by muon spin relaxation using model compounds Rb₂Co _c Mg_1−c F₄. Muon relaxation shows an anomaly at a remarkably higher temperature T _N ^μSR than the transition temperature determined by neutron Bragg scattering T _N ^ND near the percolation threshold for square lattice (c _p=0.593). The difference between the two temperatures amounts to 50% of T _N ^ND just above c _p. The field cooling effect of DC magnetic susceptibility is appreciable below T _N ^ND while the temperature of the anomaly in AC susceptibility approaches to T _N ^μSR as the frequency is increased. It was concluded that there is a crossover from two-dimensional ordering at T _N ^μSR to three-dimensional ordering at T _N ^ND but the two-dimensional order between T _N ^μSR and T _N ^ND has slow fluctuations due to the fractal structure with a plenty of weak links. This revised version was published online in September 2006 with corrections to the Cover Date.     

Microscopic theory of3He—4He solutions

The ring diagram contribution to the grand partition function of a mixture of fermions and bosons is obtained from a rigrous formula which extends the single component formula of Montroll and Ward. Together with the contributions from some other relevant graphs, it is applied to a dilute solution of³He with⁴He. For a small mass difference parameter, the ground state energy is shown to be expressed as a linear function of³He concentration. The coefficients of this energy expression are obtained explicitly for soft and hard-sphere potential models. From the energy, the differential volume coefficient is obtained also.This work was supported by ONR under Contract No. N00014-79-C-0451     

121Sb and127I Mössbauer spectroscopic study on Sb-I hypervalent bonds in trigonal bipyramidal antimony(V) complexes

Both¹²¹Sb and¹²⁷I Mössbauer parameters at 20 K were obtained for six organoantimony(V) complexes, having trigonal bipyramidal geometry around the antimony atoms. Characteristics of the apical Sb-I hypervalent bonds were deduced from the above parameters and also from the¹²¹Sb Mössbauer parameters of eight trigonal bipyramidal antimony complexes with other halogen atoms than iodine.