Reinvestigation of the absolute stereochemistry of megastigmane glucoside, icariside B(5)

Icariside B(5) is one of the widely distributed megastigmane glucosides among plant sources. The absolute structure of icariside B(5) was reinvestigated by chemical conversion from the related compound and the application of the modified Mosher's method. As a result, the structure of icariside B(5) was revised to be (6S,9S)-6,9-dihydroxymegastigman-4-en-3-one 9-O-β-D-glucopyranoside.     

A schauder decomposition and weakly singular integral equations in Lp

In this paper, a Schauder decomposition in L_p is used to obtain numerical solutions for the Fredholm integral equations of the second kind. Considerations are also given to weakly singular integral equations and two dimensional weakly singular integral equations.     

Influence of an iodine treatment on the structure and physical properties of Bombyx mori silk fibroin fiber

Silk fibroin (SF) fiber from the Bombyx mori silkworm was treated with a 1.23 N iodine/potassium iodide (I₂–KI) aqueous solution, and the structure and physical properties were investigated to elucidate the effects of the iodine treatment. The SF fiber absorbed polyiodide ions such as I and I by immersion in the I₂–KI solution, and the weight gain of the SF fiber increased with the treatment time; it became saturated at about 20 wt % after 40 h. The results of the weight gain, Fourier transform infrared spectroscopy, and X‐ray diffraction measurements suggested that polyiodide ions mainly entered the amorphous region. Moreover, a new sharp reflection in the meridional direction, corresponding to a period of 7.0 Å, was observed and indicated the possibility of the formation of a mesophase structure of β‐conformation chains. Dynamic viscoelastic measurements showed that the molecular motion of the crystalline regions at about 220 °C was enhanced and shifted to lower temperature by the introduction of polyiodide ions. This indicated that the iodine component weakened the hydrogen bonding between the SF molecules forming the β‐sheet structure and caused molecular motion of the crystal to occur more easily with heating. With heating above 270 °C, the iodine component introduced intermolecular crosslinking to SF, and the melt flow of the sample was inhibited. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3418–3426, 2006     

Transition-metal-catalyzed sequential cross-coupling of bis(iodozincio)methane and -ethane with two different organic halides

Bis(iodozincio)methane, prepared from diiodomethane and zinc, reacts with an organic halide in the presence of a transition-metal catalyst to give an iodozinciomethylenated compound; this then reacts with another organic halide to form a C--C bond. The overall process connects two electrophiles with one carbon atom. Bis(iodozincio)ethane can also undergo this transformation, yielding a new stereogenic center. The asymmetric induction of this stereogenic center was investigated by using a chiral palladium catalyst.     

Soft magnetic characteristics of an ultrathin CoFeNi free layer in spin-valve films

We have investigated the soft magnetic characteristics of an ultrathin Co-rich CoFeNi free layer in spin-valve films. By addition of Ni to a Co-rich CoFe free layer, magnetostriction (λ$\lambda$) of the films increased positively with Ni concentration, in contrast to which a Co₉₀Fe₁₀ free layer showed a negatively large λ$\lambda$. However, Ni addition also caused an increase in coercivity of the easy axis direction (H_c^e.a.). To avoid this problem, a slight decrease in the Co contents of a CoFeNi free layer was found to be effective for decreasing H_c^e.a.. In order to satisfy both the small λ$\lambda$ and H_c^e.a., a free layer of (Co₈₆Fe₁₄)₈₈₋₉₄Ni₁₂₋₆ proved to be an optimum composition in spin-valve films. Moreover, the zero λ$\lambda$ composition of the CoFeNi free layer was changed by a high-conductance Cu layer deposited on the free layer, which was considered to come from the lattice strain of a free layer.     

Hyper-Raman microspectroscopy: a new approach to completing vibrational spectral and imaging information under a microscope

We have developed hyper-Raman scattering microspectroscopy and applied it to a microcrystal of all-trans-beta-carotene. The hyper-Raman spectrum of all-trans-beta-carotene exhibits a Raman-inactive but infrared-active vibrational mode at 1564 cm(-1). Hyper-Raman imaging of a microcrystal was performed with this band. Infrared-active vibrational imaging was achieved with a spatial resolution much higher than that of conventional infrared microscopy. The combination of Raman and hyper-Raman spectroscopy opens up a new scope for high-spatial-resolution vibrational microspectroscopy that is not restricted by the selection rule.     

Dynamics of 9-hydroxyphenalenone studied by one-dimensional solid-state spin exchange NMR

We present a new NMR method to clarify the dynamics of proton tautomerism in solid 9-hydroxyphenalenone. Two 13C resonance lines influenced by the proton tautomerism have a chemical-shift difference between them, which increases with decreasing temperature. To depict the precise potential curve of the proton tautomerism, the chemical-shift difference when the proton tautomerism is completely frozen is necessary. For solid 9-hydroxyphenalenone and its derivatives, the freezing temperatures are often under -100 degrees C. When the freezing temperatures are below the temperature range in which standard magic angle spinning NMR probes can perform a sample spinning, it is very difficult to obtain the shift difference. The NMR experiments based on this new method are performed at a temperature significantly higher than -100 degrees C at which the proton tautomerism is still active. The new method yields the 13C spin relaxation rates, the rates for the proton tautomerism, and the populations of the two tautomers. Using the populations and the 13C chemical-shift difference at that temperature, we determined the chemical-shift difference at the freezing temperature. We also obtained several parameters characterizing the potential profile for the proton dynamics in solid 9-hydroxyphenalenone.     

Isomerization reaction of head-to-head alpha-pyridonato-bridged ethylenediaminepalladium(II) binuclear complex, [Pd2(en)2(C5H4NO)2]2+, in aqueous solution

Head-to-head bis(alpha-pyridonato)-bridged bis(ethylenediamine)dipalladium(ii), HH-[Pd(2)(en)(2)(alpha-pyridonato)(2)](ClO(4))(2), was synthesized and structurally characterized by X-ray crystallography. The (1)H NMR spectra show that the head-to-head (HH) dimer produces the head-to-tail (HT) dimer and monomers ([Pd(en)(alpha-pyridone)(2)](2+), [Pd(en)(H(2)O)(alpha-pyridone)](2+), [Pd(en)(H(2)O)(2)](2+), etc.) in aqueous solution, and the relative amount of dimers to monomers is dependent on the total concentration of the HH dimer dissolved as well as the acidity of the solution. It was found that the formation of the HH and HT dimers from the monomers is fast, and the HT dimer is produced from the HH dimer only via coexisting monomers, i.e., there is no direct isomerization path between the HH and HT dimers. The kinetic analyses for the HH <==>HT isomerization reaction with time-resolved (1)H NMR measurements revealed that the reaction proceeds via first-order kinetics, which was explained based on a relaxation process. The rate determining step for HH <==>HT isomerization is the reaction step between the mono-alpha-pyridone complex and the bis-alpha-pyridone complex, [Pd(en)(H(2)O)(alpha-pyridone)](2+)+alpha-pyridone <==> [Pd(en)(alpha-pyridone)(2)](2+).     

Exciton recurrence motion in aggregate systems in the presence of quantized optical fields

The exciton dynamics of model aggregate systems, dimer, trimer, and pentamer, composed of two-state monomers is computationally investigated in the presence of three types of quantized optical fields, i.e., coherent, amplitude-squeezed, and phase-squeezed fields, in comparison with the case of classical laser fields. The constituent monomers are assumed to interact with each other by the dipole-dipole interaction, and the two-exciton model, which takes into account both the one- and two-exciton generations, is employed. As shown in previous studies, near-degenerate exciton states in the presence of a (near) resonant classical laser field create quantum superposition states and thus cause the spatial exciton recurrence motion after cutting the applied field. In contrast, continuously applied quantized optical fields turn out to induce similar exciton recurrence motions in the quiescent region between the collapse and revival behaviors of Rabi oscillation. The spatial features of exciton recurrence motions are shown to depend on the architecture of aggregates. It is also found that the coherent and amplitude-squeezed fields tend to induce longer-term exciton recurrence behavior than the phase-squeezed field. These features have a possibility for opening up a novel creation and control scheme of exciton recurrence motions in aggregate systems under the quantized optical fields.