A new leishmanicidal saponin from Brunfelsia grandiflora

A new furostan-type saponin (1) was isolated from the methanolic extract of Brunfelsia grandiflora leaves, together with four known compounds. The chemical structure of 1 was determined by spectroscopic analysis and chemical reaction to be 26-O-beta-D-glucopyranosyl 22alpha-methoxyfurost-3beta,26-diol 3-O-beta-D-xylopyranosyl(1-->3)-{beta-D-glucopyranosyl(1-->2)}-beta-D-glucopyranosyl(1-->4)-beta-D-glucopyranoside. Compound 1 showed potent leishmanicidal activity in vitro against Leishmania major.     

Binding energies and electronic structures of Cu(OH2)n and Cu(NH3)n (n=1–4): anomaly of the two ligand Cu complexes

Ab initio calculations up to MP4(SDTQ) level and density functional theory have been used to estimate binding energies and electronic structures of Cu⁺(L)_n (L=OH₂, NH₃, n=1–4) complexes using TZP basis set types. The computed binding energies agree well with experimental values. General trends in structures and energetics are recorded for both Cu⁺(OH₂)_n and Cu⁺(NH₃)_n systems. The first two ligands are more strongly bound to Cu⁺ than the third and fourth molecules. The 4s–3dσ hybridization and electrostatic interactions are the main factors behind the higher binding energies for the first two ligands. Analysis of HOMO mixed orbitals in the copper ion as well as in complexes indicates shrinking of the orbital lobes directed to the ligand with shrinking more effective in the two ligand system. The lower binding energies for the third and fourth ligands were attributed to the attenuation of sdσ hybridization and decreasing of Cu–L attraction at long separation which is necessary to relieve Cu–L and L–L exchange repulsions. NBO analysis and charge-model calculations support the presence of sdσ hybridization and electron transfer to the copper ion in case of the first two ligands.     

Novel molecularly hybridized polyethylene/silica composite materials: Polymerization of ethylene with supported titanocenes by mesoporous silicates

A novel molecularly hybridized polyethylene/silica composite thin film was obtained by the gas‐phase polymerization of ethylene with a titanocene‐mounted mesoporous silica layer on a mica plate with mesoscopic pores arranged on the film surface. However, the use of titanocene‐mounted hexagonal domains of mesoporous silica on a glass plate for the gas‐phase polymerization of ethylene resulted in the formation of an islanded polyethylene/silica hybridized material. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4821–4825, 2000     

Acid-catalyzed deprotection mechanism of tert-butyloxycarbonyloxy polymers in chemically amplified resists

A mechanism of acid-catalyzed deprotection of poly(4-tert-butyloxycarbonyloxy-styrene), PBOCST, in chemically amplified resists has been elucidated in terms of elementary processes by means of semiempirical molecular orbital calculations. It is concluded that the overall deprotection of tert-butyloxycarbonyl (t-BOC) group proceeds stepwise; i.e., (a) the first products are an acid carbonate and a tert-butyl cation; (b) a phenolic compound is the secondary and final product from the acid carbonate, which is realized by assistance with a counter anion accompanied by acid; (c) the counter anion also assists acid regeneration from the tert-butyl cation to produce isobutylene. The yield rate of the phenol is proportional to the product of concentrations of the polymer, the catalytic acid, and the counter anion. The activation energy (21 kcal/mol) calculated for the rate-determining step (a) is in good agreement with an experiment. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1035–1042, 1998     

Summary of the IZEST science and aspiration

Over 30 associated laboratories across 13 countries are part of the international program known as IZEST (International center for Zetta-Exawatt Science and Technology), which has been initiated and coordinated by the École Polytechique and the CEA. Together, this collaboration of laboratories are exploring new ways to push laser peak power and intensities beyond the present horizon with the aim to perform Laser-Based High Energy Physics.     

Effect of reaction vessel diameter on sonochemical efficiency and cavitation dynamics

The influence of reaction vessel diameter on the sonochemical yield was investigated by using reaction vessels with five different diameters. It was revealed that the formation of H₂O₂ and chloride ion, from the sonolysis of pure water and 1,2,4-trichlorobenzene aqueous solution, was affected by the reaction vessel diameter. That is, these yields increased as the reaction vessel diameter increased up to ø 90 mm and then decreased over ø 90 mm. From the analyses of the measurement of sonochemiluminescence and the calorimetry, it was suggested that active cavitation bubbles were formed at certain zones. In the case of a larger diameter reaction vessel, it was suggested that bubble nuclei that have not grown up to the resonance size, escaped from the sonication zone to the non-sonication zone and dissolved away. As a result, the number of active cavitation bubbles and the yields of H₂O₂ and chloride ion would decrease in the case of a larger diameter reaction vessel.