Stereocontrolled palladium(0)-catalyzed preparation of unsaturated azidosugars: an easy access to 2- and 4-aminoglycosides

The palladium-catalyzed substitution of alkyl 4,6-di-O-acetyl-α-d-erythro-hex-2-eno-pyranosides using NaN₃ as the nucleophile gave predominantly the corresponding alkyl 2-azido-2,3,4-trideoxy-α-d-threo-hex-2-enopyranosides in the presence of Pd(PPh₃)₄. However, alkyl 6-O-acetyl-4-azido-2,3,4-trideoxy-α-d-erythro-hex-2-enopyranosides were obtained as the major products using Pd(PPh₃)₄ as the catalyst in the presence of dppb as the added ligand. Conversely, alkyl 6-O-(tert-butyldimethylsilyl)-4-O-methoxycarbonyl-2,3-dideoxy-α-d-hex-2-enopyranosides gave exclusively alkyl 4-azido-6-O-(tert-butyldimethylsilyl)-2,3,4-trideoxy-α-d-erythro-hex-2-enopyranosides in the presence of Pd₂(dba)₃/PPh₃ as the catalyst and Me₃SiN₃ as the nucleophile. The bis-hydroxylation followed by hydrogenation of ethyl 4-azido-2,3,4-trideoxy-α-d-erythro-hex-2-enopyranoside afforded the corresponding 4-amino-α-d-mannopyranoside, when propyl 2-azido-2,3,4-trideoxy-α-d-threo-hex-3-enopyranoside gave the 2-amino-α-d-altropyranoside under the same conditions.     

Cobalt as internal standard for arsenic and selenium determination in urine by simultaneous atomic absorption spectrometry

The effectiveness of internal standardization for simultaneous atomic absorption spectrometry (SIMAAS) was investigated for As and Se determination in urine. Co and Sn were selected as internal standard (IS) candidates based on the evaluation of some physico-chemical parameters related to the atomization. Correlation graphs, plotted from the normalized absorbance signals (n = 20) of internal standard (axis y) versus analyte (axis x), precision, and accuracy of the analytical results were the supportive parameters to choose Co as the most appropriate IS. The urine samples were diluted 1 + 2 to 1.0% (v/v) HNO₃ + 80 μg L⁻¹ Co²⁺. The mixture 20 μg Pd + 3 μg Mg was used as chemical modifier and the optimized temperatures for pyrolysis and atomization steps were 1400 and 2300 °C, respectively. The characteristic masses for As (47 ± 1 pg) and Se (72 ± 2 pg) were estimated from the analytical curves. The detection limits (n = 20, 3δ) were 1.8 ± 0.1 and 2.6 ± 0.1 μg L⁻¹ for As and Se, respectively. The reliability of the entire procedure was checked with the analysis of certified reference material from Sero AS(Seronorm™ Trace Elements in Urine). The obtained results showed the matrix interference disallowed the instrument calibration with aqueous standards. The best analytical condition was achieved when matrix-matched standards were used in combination with Co as IS, which improved the recoveries obtained for As. Under this experimental condition, eight urine samples were analysed and spiked with 10 and 25 μg L⁻¹ As and Se. The mean recoveries were 96 ± 6% (10 μg L⁻¹ As), 95 ± 6% (25 μg L⁻¹ As), 101 ± 7% (10 μg L⁻¹ Se), and 97 ± 4% (25 μg L⁻¹ Se).     

Optimization of enzymatic production of biodiesel from castor oil in organic solvent medium

We studied the production of fatty acid ethyl esters from castor oil using n-hexane as solvent and two commercial lipases, Novozym 435 and Lipozyme IM, as catalysts. For this purpose, a Taguchi experimental design was adopted considering the following variables: temperature (35–65°C), water (0–10 wt/wt%), and enzyme (5–20 wt/wt%) concentrations and oil-to-ethanol molar ratio (1∶3 to 1∶10). An empirical model was then built so as to assess the main and cross-variable effects on the reaction conversion and also to maximize biodiesel production for each enzyme. For the system containing Novozym 435 as tatalyst the maximum conversion obtained was 81.4% at 65°C, enzyme concentration of 20 wt/wt%, water concentration of 0 wt/wt%, and oil-to-ethanol molar ratio of 1∶10. When the catalyst was Lipozyme IM, a conversion as high as 98% was obtained at 65°C, enzyme concentration of 20 wt/wt%, water concentration of 0 wt/wt%, and oil-to-ethanol molar ratio of 1∶3.     

Bis(trimethylsilyl)amide und -methanide des Yttriums — Molekülstrukturen von Tris(diethylether-O)lithium-(μ-chloro)-tris[bis(trimethylsilyl) methyl]yttriat,solvensfreiem Yttrium-tris[bis(trimethylsilyl)amid] sowie dem Bis(benzonitril)-Komplex

Bis(trimethylsilyl)amides and -methanides of Yttrium — Molecular Structures of Tris(diethylether-O)lithium-(μ-chloro)-tris[bis(trimethylsilyl)methyl]yttriate, solvent-free Yttrium Tris[bis(trimethylsilyl)amide] as well as the Bis(benzonitrile) Complex The reaction of yttrium(III) chloride with the three-fold molar amount of LiE(SiMe₃)₂ (E = N, CH) yields the corresponding yttrium derivatives. Yttrium tris-[bis(trimethylsilyl)amide] crystallizes in the space group P3 1c with a = 1 636,3(2), c = 849,3(2) pm, Z = 2. The yttrium atom is surrounded trigonal pyramidal by three nitrogen atoms with Y? N-bond lengths of 222 pm. Benzene molecules are incorporated parallel to the c-axes. The compound with E = CH crystallizes as a (Et₂O)₃LiCl-adduct in the monoclinic space group P2₁/n with a = 1 111,8(2), b = 1 865,2(6), c = 2 598,3(9) pm, β = 97,41(3)° and Z = 4. The reaction of yttrium tris[bis(trimethylsilyl)amide] with benzonitrile yields the bis(benzonitrile) complex, which crystallizes in the triclinic space group P1 with a = 1 173,7(2), b = 1 210,3(2), c = 1 912,4(3) pm, α = 94,37(1), β = 103,39(1), γ = 117,24(1)° and Z = 2. The amido ligands are in equatorial, the benzonitrile molecules in axial positions.     

Synthesis and structural characterization of fac-BrMn(CO)3{PH(C6H5)2}2

In attempts to find appropriated methods for preparation of unstable sulfinyl and sulfonylphosphane complexes we have synthesized the diphenylphosphine complexes of Mn(I), BrMn(CO)₄PHPh₂, (1) and BrMn(CO)₃(PHPh₂)₂ (2). Both should undergo electrophilic substitution in the presence of an adequated base. Parallel to the reactions of stabilization of phosphanes we have studied by means of x-ray analysis the structure of fac-BrMn(CO)₃(PHPh₂)₂ (2). The compound crystallizes in the triclinic space group P, a = 9.840(2), b = 11.207(2), c = 13.083(3) Å, = 72.00(3), = 69.59(3), = 81.41(3)°, U = 1284.7(4) ų, and Z = 2. In this complex the manganese atom shows an octahedral coordination geometry, with three carbonyl ligands in a fac arrangement, and one bromide and two diphenylphosphine ligands cis to each other.     

Bone architecture analyses of rat femur with 3D microtomographics images

Summary One of the great 3D micro tomography (3D-mCT) applications in the medical area is the characterization of bone architecture, especially when it is spoken in osteoporosis because, among other factors, is characterized by the deterioration of the architecture. This work shows the 3D quantification, based on stereological concepts, of the bone tissue through 3D-mCT in real time. The analyses were carried out in femur rat and the 3D visualizations helped to understand bones morphology. The results showed the potential of this computational technique to verify the capability of characterization of the internal bone structures and the importance of the threshold level in the binarization process.     

Degradation of polyamide 11 in rotational moulding

The degradation of polyamide 11 (PA 11) was studied in samples rotationally moulded using a range of processing temperatures. The chemical changes occurring in the moulded material were assessed using FTIR, UV-vis spectroscopy, ¹H NMR spectroscopy, gas chromatography, rheometry and microscopy. The results showed that the degradation is complex and depends on the location of the material in the moulding. At the internal surface, the degradation is predominantly thermo-oxidative leading to the formation of carbon dioxide, carboxylic acids and conjugated unsaturated oligo-enimines (UV-vis-active chromophores). Away from the internal surface, the dominant process is through the recombination of broken chains and/or post-condensation reactions that increase the molecular weight without the formation of UV-vis-active chromophores. A degradation mechanism is proposed for PA 11 in rotational moulding.     

Nonequilibrium model for the contact process in an ensemble of constant particle number.

We introduce and analyze numerically a nonequilibrium model with a conserved dynamics which is a realization of the contact process in an ensemble of constant particle number. The model possesses just one process in which particles jump around landing only on empty sites next to an existing particle. Particles are not allowed to land on a vacant site surrounded by empty sites. In contrast with the ordinary contact process, the present model does not have an absorbing state. In spite of lacking an absorbing state, the model displays properties that, in the thermodynamic limit, are identical to those of the ordinary contact process.     

Fragmentation experiment and model for falling mercury drops

The experiment consists of counting and measuring the size of the many fragments observed after the fall of a mercury drop on the floor. The size distribution follows a power-law for large enough fragments. We address the question of a possible crossover to a second, different power-law for small enough fragments. Two series of experiments were performed. The first uses a traditional film photographic camera, and the picture is later treated on a computer in order to count the fragments and classify them according to their sizes. The second uses a modern digital camera. The first approach has the advantage of a better resolution for small fragment sizes. The second, although with a poorer size resolution, is more reliable concerning the counting of all fragments up to its resolution limit. Both together clearly indicate the real existence of the quoted crossover.     

Thermal stability of fluorochloroindate glasses

New fluorindate glass compositions have been investigated in order to improve optical transmission as well as thermal properties. Chloride inclusion extends transmission of a fluoride matrix to longer wavelength in infrared region. In the present work thermal parameters of an IZnBS composition, based on InF₃, ZnF₂, BaF₂ and SrF₂, with various amounts of alkaline chlorides were investigated by differential scanning calorimetry. The chloride presence decreased all characteristic temperatures and increased both thermal stability and glass forming ability up to 10% of MCl content, where M=Li, Na, K and Rb. The presence of NaCl promoted glass phase separation. For samples containing same concentration of NaCl, this effect is accentuated for increasing the contents of SrF₂. This revised version was published online in August 2006 with corrections to the Cover Date.