Determination of Pb,Zr, Ti,Sr, Cr,Nb and La in lead zirconate titanate ceramics by particle‐induced X‐ray emission

A particle‐induced X‐ray emission (PIXE) technique has been used in the determination of the principal components Pb, Zr and Ti and the substituting elements Sr, Cr, Nb and La in lead zirconate titanate ceramics. In general, precision of analysis was concentration dependent from each element under study. For Pb, precision varied between 0.13% and 0.16%, at higher concentration of 59.32–64.5%. It was around 6–9% for Sr, Cr and Nb at concentrations of 1% or lower. Particular attention was devoted to the estimation of the analysis trueness. With this purpose, three methods were applied: (1) comparison of PIXE and inductively coupled plasma optical emission spectrometry concentrations, (2) recovery study and (3) comparison with a laboratory standard. Trueness of analysis was around 100 ± 10% for the evaluated elements Pb, Zr, Ti, Sr and Cr. The expected stoichiometry and elemental composition homogeneity of a wide group of produced ceramics were confirmed by the PIXE technique. Copyright © 2012 John Wiley & Sons, Ltd.     

N1,N1-Diethyl-N2-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)acet­amidine

The solid-state conformation of the title compound, C₂₀H₃₂N₂O₉, has been determined at 150 K. The pyran­ose ring has a distorted chair conformation. Among the possible conformations of the C—N glycosidic bond, that of the E rotamer is observed and a short intramolecular C_methyl⋯O contact may partly stabilize this conformation. Crystal cohesion is stabilized by an extensive network of weak C—H⋯O hydrogen bonds and close contacts.     

Regioselective enzymatic acylations of polyhydroxylated eudesmanes: semisynthesis, theoretical calculations, and biotransformation of cyclic sulfites

Different lipase enzymes have been tested in order to perform regioselective acetylations on the eudesmane tetrol from vulgarin. High yields (95%) of 1,12-diacetoxy derivative (4) were achieved in 1 h with Candida antarctica lipase (CAL). However, only the 12-acetyl derivative (6) was obtained in similar yield with Mucor miehei (MML) or Candida cylindracea (CCL) lipases. The enzymatic protection at C-1 and C-12 has been used to form eudesmane cyclic-sulfites between C-6 and C-4 atoms. The R/S-sulfur configuration has been assigned by means of the experimental and theoretical (13)C and (1)H NMR chemical shifts. The theoretical shifts were calculated using the GIAO method, with a MM+ geometry optimization followed by a single-point calculation at the B3LYP/6-31G(*) level (B3LYP/6-31G(*)//MM+). Moreover, B3LYP/6-31G(*) geometry optimizations were carried out to test the B3LYP/6-31G(*)//MM+ results, for the deacetylated sulfites (12 and 15). In addition to the delta(C) and delta(H) shifts, the (3)J(HH) coupling constants were also calculated and compared with the experimental values when available. Finally, different reactivities have been checked in both sulfites by biotransformation with Rhizopus nigricans. While the R-sulfite gave 2 alpha- and 11 beta-hydroxylated metabolites, the S-sulfite yielded only regioselective deacetylations. Furthermore, both sulfites showed different reactivities in redox processes.     

Semi-empirical traction prediction equations based on relevant soil parameters

Extensive single-wheel traction tests were conducted in the vicinity of UC Davis campus using four different radial ply tires, two soil types, four soil conditions, three levels of inflation pressures, and three axle loads. Soil sinkage and shear characteristics were also obtained using an instrumented soil test device in every test condition. These field data were analyzed to obtain semi-empirical traction prediction equations for radial ply tires. In general, these prediction equations were able to predict traction equation parameters with less than 25% error.     

Reactivity of Chiral Sesquiterpene Synthons Obtained by the Degradation of Maslinic Acid from Olive‐Pressing Residues

Maslinic acid, a naturally occurring compound isolated from the solid wastes of olive‐oil pressing, was fragmented through the C‐ring via oxidative procedures to obtain two structural fragments. The chemical behaviors of cis‐decalin, from the D and E rings, and of trans‐decalin fragments, from the A and B rings, were investigated in depth using several chemical and enzymatic reactions. These decalin chiral synthons are interesting intermediates to semisynthesize phenanthrene‐ and drimane‐type compounds and natural tricyclic triterpenes.     

Remote hydroxylation of methyl groups by regioselective cyclopalladation. Partial synthesis of hyptatic acid-A

Hyptatic acid-A (32), a 2alpha,3beta,24-trihydroxyolean-12-en-28-oic acid, previously isolated from Hyptis capitata, was obtained from maslinic acid (2). The regioselective cyclopalladation of the axial methyl group on C-4 of maslinic acid afforded the C-24 hydroxymethylene group due to the presence of a C-2-OR substituent. Nevertheless, hederagenin (7) (23-hydroxy derivative) was formed when this oxygenated group was not present.     

Kinetic spectroscopy of triplet states of benzenoid hydrocarbons using modulated Hg resonance radiation

Triplet—triplet absorption spectra in the 220–250 nm region, and rate constants for unimolecular and bimolecular decay of the lowest triplet states of simply substituted benzenes in the gas phase have been obtained using a phase modulation technique. For deuterium and methyl substitution, first order decay constants are of the same order as in benzene of 10³ s^?1, with second order decay constants of the order of 10⁷ ? mol^?1 s^?1, also as in benzene. For trifluoromethyl substitution, these rate constants increase dramatically to of the order of 10^?5 s^?1 and 10⁸ ? mol^?1 s^?1 respectively, and fluorine substitution is even more dramatic, with values in the 10⁶ s^?1 and 10⁹ ? mol^?1 s^?1 respectively.