Structure of porous vycor glass and its adsorption characteristics of water —An application of positron annihilation method

Positron lifetimes in porous Vycor glass have been measured. There are four lifetime components, and the fourth component has been assigned too-Ps annihilation in large pores of radius 34 Å. The intensityI ₄ has been correlated to a specific surface area, but the value obtained fromI ₄ by the Monte Carlo method is smaller than that obtained by the BET method. From variations in (τ₄,I ₄) against the kinetics of adsorption of water vapor, a rough picture of water adsorption is presented.     

Aq-difference analogue of U(g) and the Yang-Baxter equation

Aq-difference analogue of the universal enveloping algebra U(g) of a simple Lie algebra g is introduced. Its structure and representations are studied in the simplest case g=sl(2). It is then applied to determine the eigenvalues of the trigonometric solution of the Yang-Baxter equation related to sl(2) in an arbitrary finite-dimensional irreducible representation.     

High-resolution infrared spectrum of hydrazoic acid: The ν3 fundamental by a tunable diode laser

The HNN bending fundamental ν₃ of HNNN, and a-type band, was measured by a tunable diode laser with Doppler limited resolution. The Stark modulation technique was used to confirm the assignment. The assignment of Q branches was revised, and the origins, effective B and D values for each subband, were determined accurately. The K dependence of these subband origin parameters, B and D, was found quite anomalous. Possible interactions are discussed.     

Solvable lattice models whose states are dominant integral weights of A it−1 (1)

A new hierarchy of solvable IRF models is presented. It is generated from Belavin's Z _n ×Z _n symmetric model. The site variables take values in the set of level l dominant integral weights of A _–1 ⁽¹⁾ . It is conjectured that the local state probabilities are given through the irreducible decomposition of characters for the affine Lie algebra pair (A _n–1 ⁽¹⁾ A _n–1 ⁽¹⁾ ,A _n–1 ⁽¹⁾ ).     

The mechanism of the chapman rearrangement of N-arylbenzimidate on the basis of the molecular structure established by X-ray. Part II

Dibenz[c,h]acridine ( 13 ) was formed directly by the Chapman rearrangement of 2-methoxycarbonyl-1-naphthyl-N-1′-naphthylbenzimidate ( 11 ) without isolation of intermediate 12 . When the Chapman rearrangement was carried out under mild reaction conditions, the intermediate 12 was isolated in high yield, whose structure was determined by the X-ray studies. The mechanism of the Chapman rearrangement can be interpreted on the basis of the X-ray data of 11 and 12 .     

Syntheses of gramicidin s analogs containing D-Serine or a dehydroalanine residue,and asymmetric hydrogenation of the dehydroalanine

Gramicidin S (GS) analogs, (D-Ser(Bzl)^4,4′]-GS ($\text{17}$), [D-Ser^4,4′]-GS ($\text{18}$), and [L-Orn(Boc)^2,2′,D-Ser^4,4′]-GS ($\text{19}$) were synthesized and $\text{17}$ showed high antibacterial activity. One residue of D-Ser in $\text{19}$ was converted asymmetrically to D-Ala via α,β-dehydroalanine.     

Lissoclibadin 1, a novel trimeric sulfur-bridged dopamine derivative, from the tropical ascidian Lissoclinum cf. badium

A novel tribenzotetrathiepin alkaloid, named lissoclibadin 1 (1), has been isolated from the ascidian Lissoclinum sp. (cf. L. badium Monniot and Monniot, 1996). The gross structure was assigned on the basis of the spectral data, and one of two possible isomers was selected by the computational modeling study. Lissoclibadin 1 inhibited the growth of the marine bacterium Ruegeria atlantica (15.2 mm at 20 μg/disk).     

Synthesis of cross-linked core-shell polymer particles by free-radical dispersion copolymerization of 4-vinylpyridine with polystyrene macromonomers in nonaqueous media

Cross-linked core-shell polymer particles were synthesized by free-radical dispersion copolymerization of 4-vinylpyridine (4VP) and various kinds of cross-linking reagents with methacryloyl-terminated polystyrene (PS) macromonomers in nonaqueous media such as 1,4-dioxane and cyclohexane. Well-defined particles were obtained by copolymerization of 4VP with ethylene glycol dimethacrylate (EGDM) in a dioxane medium. The particle diameters (D(n)=40-990 nm) decreased drastically both with increasing the feed concentration ratio of macromonomer to 4VP, [PS-M]/[4VP], and with increasing molecular weight of PS-M macromonomers. The particle size distribution (D(w)/D(n)) was in the range 1.02-1.10. PS-M macromonomers acted not only as comonomers but also as stabilizers. The particle diameters obtained in dioxane were smaller than those obtained in cyclohexane. Thus, we observed a tendency to smaller particle size as the media became more soluble for PS-M macromonomer.     

Quantitative evaluation of weak nonbonded Se...F interactions and their remarkable nature as orbital interactions

To evaluate weak intramolecular nonbonded Se...F interactions recently characterized for a series of o-selenobenzyl fluoride derivatives (Iwaoka et al., Chem. Lett. 1998, 969-970), the temperature dependence of the nuclear spin coupling between Se and F (J(Se...F)) was investigated for 2-(fluoromethyl)phenylselenenyl cyanate (1a) and bis[2-(fluoromethyl)phenyl] diselenide (1e) in CD2Cl2 and CD3CN. A significant increase in the magnitude of J(Se...F) was observed for both 1a and 1e upon lowering temperature, whereas the values of J(Se...F) for the corresponding trifluoromethyl compounds slightly reduced or remained unchanged at low temperatures. Application of the rapid equilibrium model between two possible conformers revealed that conformer A with an intramolecular Se...F interaction is more stable in enthalpy (DeltaH) by 1.23 kcal/mol for 1a (in CD2Cl2) and by 0.85 and 0.83 kcal/mol for 1e (in CD2Cl2 and CD3CN, respectively) than conformer B, which does not have close Se...F contact. The negligible solvent effects for 1e suggested marginal electrostatic nature of the Se...F interactions. Instead, importance of the n(F) -->sigma*(Se-X) orbital interaction was suggested by quantum chemical (QC) calculations and the natural bond orbital (NBO) analysis.